Remove HeapProfiler.finishHeapSnapshot event from remote debugging protocol

This event is redundant as it is sent right before the response to HeapProfiler.getHeapSnapshot command. The command response should be used instead of the event.

BUG=306475
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/27000005

git-svn-id: svn://svn.chromium.org/blink/trunk@159652 bbb929c8-8fbe-4397-9dbb-9b2b20218538