Now that CpuProfiler sends does sampling on the profile event processing thread there is no need to launch sampler thread. The latter is used only for --prof profiler.

BUG=v8:2814
R=bmeurer@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/23011029

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16430 ce2b1a6d-e550-0410-aec6-3dcde31c8c00