Revert "Implement Object.getNotifier(obj).performChange()" (r14696)

Reverts r14696 because it caused debug assertion failures when running
test/mjsunit/harmony/object-observe.js

TBR=rossberg

Review URL: https://codereview.chromium.org/15203002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14697 ce2b1a6d-e550-0410-aec6-3dcde31c8c00