Do not store last collected profile in InspectorProfilerAgent

V8's bug that caused CPU profile recording to stop if last finihsed profile was removed was fixed (https://code.google.com/p/v8/source/detail?r=18302) and it is time to remove the workaround.

BUG=327298
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/118563004

git-svn-id: svn://svn.chromium.org/blink/trunk@164284 bbb929c8-8fbe-4397-9dbb-9b2b20218538