Revert "Send SIGPROF signals on the profiler event processor thread"

This reverts commit r13735 as CPU profiler data is inaccurate after that change.

BUG=v8:2571

Review URL: https://codereview.chromium.org/12592002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13851 ce2b1a6d-e550-0410-aec6-3dcde31c8c00