This reverts commit 651c90409ee7b8f43da7d1c60fcb172f1ad51901.
With this change applied, test/widgets/widget_inspector_test.dart is failing
when run by the dev/bots/test.dart script in the framework tree.
This improves performance as the version in the SDK is able to work more
incrementally and avoids creating an expensive ClassHierarchy.
There is now no measureable performance difference with the option so the
kernel transformer can be enabled by default.
