Revert "Address additional analysis issues in the observatory codebase."

runtime/observatory/tests/observatory_ui/mocks/objects/isolate.dart

Index: runtime/observatory/tests/observatory_ui/mocks/objects/isolate.dart
diff --git a/runtime/observatory/tests/observatory_ui/mocks/objects/isolate.dart b/runtime/observatory/tests/observatory_ui/mocks/objects/isolate.dart
index 310e8fbfa012074ca521d23ab36d3814592967f6..fa841307284410a8b3a9c00983451af3ca051d3d 100644
--- a/runtime/observatory/tests/observatory_ui/mocks/objects/isolate.dart
+++ b/runtime/observatory/tests/observatory_ui/mocks/objects/isolate.dart
@@ -53,8 +53,4 @@ class IsolateMock implements M.Isolate {
       this.pauseEvent,
       this.rootLibrary,
       this.entry});
-
-  Future collectAllGarbage() async {
-    throw "Unimplemented";
-  }
 }