Remove StrongTypeSystemImpl.

It was deprecated in analyzer version 0.34.0, and clients are no
longer using it.

Change-Id: Ib27e9173eb57bcbec700071bd69acbcfaf96e913
Reviewed-on: https://dart-review.googlesource.com/c/91112
Commit-Queue: Paul Berry <paulberry@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Auto-Submit: Paul Berry <paulberry@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/pkg/analyzer/CHANGELOG.md b/pkg/analyzer/CHANGELOG.md
index fc5e6b4..f7ff184 100644
--- a/pkg/analyzer/CHANGELOG.md
+++ b/pkg/analyzer/CHANGELOG.md
@@ -8,6 +8,7 @@
 * Removed `EMPTY_LIST` constants.  Please use `const <...>[]` instead.
 * Disabled support for the task model.  Please use the new `AnalysisSession`
   API.
+* Removed `StrongTypeSystemImpl`.  Please use `Dart2TypeSystem` instead.
 
 ## 0.34.2
 * Removed support for the `@checked` annotation.  Please use the `covariant`
diff --git a/pkg/analyzer/lib/src/generated/type_system.dart b/pkg/analyzer/lib/src/generated/type_system.dart
index 05a7719..0a792c4 100644
--- a/pkg/analyzer/lib/src/generated/type_system.dart
+++ b/pkg/analyzer/lib/src/generated/type_system.dart
@@ -1662,14 +1662,6 @@
 }
 
 /**
- * A type system that implements the type semantics for strong mode.
- */
-@deprecated
-class StrongTypeSystemImpl extends Dart2TypeSystem {
-  StrongTypeSystemImpl(TypeProvider typeProvider) : super(typeProvider);
-}
-
-/**
  * The interface `TypeSystem` defines the behavior of an object representing
  * the type system.  This provides a common location to put methods that act on
  * types but may need access to more global data structures, and it paves the