Revert "First step towards having patch files for generic libraries."

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index 0a81f15e6eeb98a6fae2dd910a7dd06cb4e3ea8f..5719f01839f8d2243808af307787dabd3ab14bf1 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -156,9 +156,6 @@ class MockCompiler extends Compiler {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
-  // The mock library doesn't need any patches.
-  Uri resolvePatchUri(String dartLibraryName) => null;
-
   Script readScript(Uri uri, [ScriptTag node]) {
     String code = sources[uri.toString()];
     if (code === null) throw new IllegalArgumentException(uri);