Remove `Utf8Decoder._convertIntercepted` hook

Fixes #54018.

Tested: existing tests.
Change-Id: I0d0cbc414a239bfc00c023ac8b9313c6f413ba83
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/337540
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>
diff --git a/sdk/lib/_internal/js_shared/lib/convert_utf_patch.dart b/sdk/lib/_internal/js_shared/lib/convert_utf_patch.dart
index d50fead..234d427 100644
--- a/sdk/lib/_internal/js_shared/lib/convert_utf_patch.dart
+++ b/sdk/lib/_internal/js_shared/lib/convert_utf_patch.dart
@@ -13,13 +13,6 @@
   Converter<List<int>, T> fuse<T>(Converter<String, T> next) {
     return super.fuse(next);
   }
-
-  // TODO(54018): Deprecate this hook.
-  @patch
-  static String? _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int? end) {
-    return null; // This call was not intercepted.
-  }
 }
 
 @patch
diff --git a/sdk/lib/_internal/vm/lib/convert_patch.dart b/sdk/lib/_internal/vm/lib/convert_patch.dart
index a9c2bd9..9a9ee1e 100644
--- a/sdk/lib/_internal/vm/lib/convert_patch.dart
+++ b/sdk/lib/_internal/vm/lib/convert_patch.dart
@@ -49,13 +49,6 @@
     // TODO(lrn): Recognize a fused decoder where the next step is JsonDecoder.
     return super.fuse<T>(next);
   }
-
-  // Allow intercepting of UTF-8 decoding when built-in lists are passed.
-  @patch
-  static String? _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int? end) {
-    return null; // This call was not intercepted.
-  }
 }
 
 class _JsonUtf8Decoder extends Converter<List<int>, Object?> {
diff --git a/sdk/lib/_internal/wasm/lib/convert_patch.dart b/sdk/lib/_internal/wasm/lib/convert_patch.dart
index 001fcec..68f92dc 100644
--- a/sdk/lib/_internal/wasm/lib/convert_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/convert_patch.dart
@@ -35,12 +35,6 @@
     // TODO(lrn): Recognize a fused decoder where the next step is JsonDecoder.
     return super.fuse<T>(next);
   }
-
-  @patch
-  static String? _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int? end) {
-    return null;
-  }
 }
 
 class _JsonUtf8Decoder extends Converter<List<int>, Object?> {
diff --git a/sdk/lib/_internal/wasm_js_compatibility/lib/convert_patch.dart b/sdk/lib/_internal/wasm_js_compatibility/lib/convert_patch.dart
index 08d920a..1ab6472 100644
--- a/sdk/lib/_internal/wasm_js_compatibility/lib/convert_patch.dart
+++ b/sdk/lib/_internal/wasm_js_compatibility/lib/convert_patch.dart
@@ -27,12 +27,6 @@
   Converter<List<int>, T> fuse<T>(Converter<String, T> next) {
     return super.fuse(next);
   }
-
-  @patch
-  static String? _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int? end) {
-    return null;
-  }
 }
 
 //// Implementation ///////////////////////////////////////////////////////////
diff --git a/sdk/lib/convert/utf.dart b/sdk/lib/convert/utf.dart
index 1cbdec4..5bd60d8 100644
--- a/sdk/lib/convert/utf.dart
+++ b/sdk/lib/convert/utf.dart
@@ -345,16 +345,8 @@
   ///
   /// If the [codeUnits] start with the encoding of a
   /// [unicodeBomCharacterRune], that character is discarded.
-  String convert(List<int> codeUnits, [int start = 0, int? end]) {
-    // Allow the implementation to intercept and specialize based on the type
-    // of codeUnits.
-    var result = _convertIntercepted(_allowMalformed, codeUnits, start, end);
-    if (result != null) {
-      return result;
-    }
-
-    return _Utf8Decoder(_allowMalformed).convertSingle(codeUnits, start, end);
-  }
+  String convert(List<int> codeUnits, [int start = 0, int? end]) =>
+      _Utf8Decoder(_allowMalformed).convertSingle(codeUnits, start, end);
 
   /// Starts a chunked conversion.
   ///
@@ -374,9 +366,6 @@
   Stream<String> bind(Stream<List<int>> stream) => super.bind(stream);
 
   external Converter<List<int>, T> fuse<T>(Converter<String, T> next);
-
-  external static String? _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int? end);
 }
 
 // UTF-8 constants.