Remove MallocStatistics and its friends

This patch removes the following unused classes:
1) MallocStatistics,
2) FastMallocStatistics
3) V8MallocStatistics

This patch also removes the now useless test,
fastmallocstatistics-object.html, and removes
mallocHeapResults from the performance test runner.

R=abarth,cevans

Review URL: https://codereview.chromium.org/435213003

git-svn-id: svn://svn.chromium.org/blink/trunk@179557 bbb929c8-8fbe-4397-9dbb-9b2b20218538