Drop globals.h include from platform.h

Also delete dead cpu-features-implied-by-platform code.

BUG=none
R=jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/326333002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21779 ce2b1a6d-e550-0410-aec6-3dcde31c8c00