Revert "Roll clang with fix for ABI change (#44711)"

This reverts commit f2cb42aa90ba3cc3b51242904021a6a7e735048f.
diff --git a/DEPS b/DEPS
index cb4c6e6..9ab1685 100644
--- a/DEPS
+++ b/DEPS
@@ -39,7 +39,7 @@
   # The list of revisions for these tools comes from Fuchsia, here:
   # https://fuchsia.googlesource.com/integration/+/HEAD/toolchain
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
-  'clang_version': 'git_revision:020d2fb7711d70e296f19d83565f8d93d2cfda71',
+  'clang_version': 'git_revision:6d667d4b261e81f325756fdfd5bb43b3b3d2451d',
 
   # The goma version and the clang version can be tightly coupled. If goma
   # stops working on a clang roll, this may need to be updated using the value
diff --git a/ci/licenses_golden/licenses_flutter b/ci/licenses_golden/licenses_flutter
index 8598c28..5721623 100644
--- a/ci/licenses_golden/licenses_flutter
+++ b/ci/licenses_golden/licenses_flutter
@@ -2582,7 +2582,6 @@
 ORIGIN: ../../../flutter/shell/platform/common/text_input_model.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/text_input_model.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/text_range.h + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/shell/platform/darwin/common/availability_version_check.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/buffer_conversions.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/buffer_conversions.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/command_line.h + ../../../flutter/LICENSE
@@ -5337,7 +5336,6 @@
 FILE: ../../../flutter/shell/platform/common/text_input_model.cc
 FILE: ../../../flutter/shell/platform/common/text_input_model.h
 FILE: ../../../flutter/shell/platform/common/text_range.h
-FILE: ../../../flutter/shell/platform/darwin/common/availability_version_check.cc
 FILE: ../../../flutter/shell/platform/darwin/common/buffer_conversions.h
 FILE: ../../../flutter/shell/platform/darwin/common/buffer_conversions.mm
 FILE: ../../../flutter/shell/platform/darwin/common/command_line.h
diff --git a/shell/platform/darwin/common/BUILD.gn b/shell/platform/darwin/common/BUILD.gn
index 7d844b7..2a59b82 100644
--- a/shell/platform/darwin/common/BUILD.gn
+++ b/shell/platform/darwin/common/BUILD.gn
@@ -13,7 +13,6 @@
   cflags_objcc = flutter_cflags_objcc
 
   sources = [
-    "availability_version_check.cc",
     "buffer_conversions.h",
     "buffer_conversions.mm",
     "command_line.h",
diff --git a/shell/platform/darwin/common/availability_version_check.cc b/shell/platform/darwin/common/availability_version_check.cc
deleted file mode 100644
index 67514cb..0000000
--- a/shell/platform/darwin/common/availability_version_check.cc
+++ /dev/null
@@ -1,48 +0,0 @@
-// Copyright 2013 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include <dispatch/dispatch.h>
-#include <dlfcn.h>
-#include <cstdint>
-
-#include "flutter/fml/logging.h"
-
-// See context in https://github.com/flutter/flutter/issues/132130 and
-// https://github.com/flutter/engine/pull/44711.
-
-// TODO(zanderso): Remove this after Clang 18 rolls into Xcode.
-// https://github.com/flutter/flutter/issues/133203
-
-namespace {
-
-typedef uint32_t dyld_platform_t;
-
-typedef struct {
-  dyld_platform_t platform;
-  uint32_t version;
-} dyld_build_version_t;
-
-typedef bool (*AvailabilityVersionCheckFn)(uint32_t count,
-                                           dyld_build_version_t versions[]);
-
-AvailabilityVersionCheckFn AvailabilityVersionCheck;
-
-dispatch_once_t DispatchOnceCounter;
-
-void InitializeAvailabilityCheck(void* unused) {
-  if (AvailabilityVersionCheck) {
-    return;
-  }
-  AvailabilityVersionCheck = reinterpret_cast<AvailabilityVersionCheckFn>(
-      dlsym(RTLD_DEFAULT, "_availability_version_check"));
-  FML_CHECK(AvailabilityVersionCheck);
-}
-
-extern "C" bool _availability_version_check(uint32_t count,
-                                            dyld_build_version_t versions[]) {
-  dispatch_once_f(&DispatchOnceCounter, NULL, InitializeAvailabilityCheck);
-  return AvailabilityVersionCheck(count, versions);
-}
-
-}  // namespace
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterAppDelegateTest.mm b/shell/platform/darwin/macos/framework/Source/FlutterAppDelegateTest.mm
index 6b13959..b58e5e7 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterAppDelegateTest.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterAppDelegateTest.mm
@@ -46,9 +46,7 @@
       [[AppDelegateTestFlutterAppLifecycleDelegate alloc] init];
   [appDelegate addApplicationLifecycleDelegate:delegate];
 
-  NSURL* URL = [NSURL URLWithString:@"https://flutter.dev"];
-  EXPECT_NE(URL, nil);
-  NSArray<NSURL*>* URLs = @[ URL ];
+  NSArray<NSURL*>* URLs = @[ [NSURL URLWithString:@"https://flutter.dev"] ];
   [appDelegate application:NSApplication.sharedApplication openURLs:URLs];
 
   EXPECT_EQ([delegate receivedURLs], URLs);
@@ -63,9 +61,7 @@
   [appDelegate addApplicationLifecycleDelegate:firstDelegate];
   [appDelegate addApplicationLifecycleDelegate:secondDelegate];
 
-  NSURL* URL = [NSURL URLWithString:@"https://flutter.dev"];
-  EXPECT_NE(URL, nil);
-  NSArray<NSURL*>* URLs = @[ URL ];
+  NSArray<NSURL*>* URLs = @[ [NSURL URLWithString:@"https://flutter.dev"] ];
   [appDelegate application:NSApplication.sharedApplication openURLs:URLs];
 
   EXPECT_EQ([firstDelegate receivedURLs], URLs);