Revert "Add error for mixins defining conflicting private names (issue 28809)"

pkg/analyzer/test/generated/compile_time_error_code_test.dart

Index: pkg/analyzer/test/generated/compile_time_error_code_test.dart
diff --git a/pkg/analyzer/test/generated/compile_time_error_code_test.dart b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
index 614f720ff694c6cb324ba0e8d39546a99b430bbe..3c95c9da539709978d5e16b8590aa375545af459 100644
--- a/pkg/analyzer/test/generated/compile_time_error_code_test.dart
+++ b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
@@ -5263,95 +5263,6 @@ f() {
     verify([source]);
   }
 
-  test_privateCollisionInMixinApplication_mixinAndMixin() async {
-    addNamedSource(
-        '/lib1.dart',
-        '''
-class A {
-  int _x;
-}
-
-class B {
-  int _x;
-}
-''');
-    Source source = addSource('''
-import 'lib1.dart';
-class C extends Object with A, B {}
-''');
-    await computeAnalysisResult(source);
-    assertErrors(
-        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
-    verify([source]);
-  }
-
-  test_privateCollisionInMixinApplication_mixinAndMixin_indirect() async {
-    addNamedSource(
-        '/lib1.dart',
-        '''
-class A {
-  int _x;
-}
-
-class B {
-  int _x;
-}
-''');
-    Source source = addSource('''
-import 'lib1.dart';
-class C extends Object with A {}
-class D extends C with B {}
-''');
-    await computeAnalysisResult(source);
-    assertErrors(
-        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
-    verify([source]);
-  }
-
-  test_privateCollisionInMixinApplication_superclassAndMixin() async {
-    addNamedSource(
-        '/lib1.dart',
-        '''
-class A {
-  int _x;
-}
-
-class B {
-  int _x;
-}
-''');
-    Source source = addSource('''
-import 'lib1.dart';
-class C extends A with B {}
-''');
-    await computeAnalysisResult(source);
-    assertErrors(
-        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
-    verify([source]);
-  }
-
-  test_privateCollisionInMixinApplication_superclassAndMixin_same() async {
-    addNamedSource(
-        '/lib1.dart',
-        '''
-class A {
-  int _x;
-}
-
-class B {
-  int _x;
-}
-''');
-    Source source = addSource('''
-import 'lib1.dart';
-class C extends A with A {}
-''');
-    await computeAnalysisResult(source);
-    assertErrors(
-        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
-    verify([source]);
-  }
-
   test_privateOptionalParameter() async {
     Source source = addSource("f({var _p}) {}");
     await computeAnalysisResult(source);