Cleaned up deopt reason messages a bit.

They are now a bit more consistent, and they don't mention the name of a
flag, which will go out of sync some day. ;-)

R=machenbach@chromium.org

Review URL: https://codereview.chromium.org/23845003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16514 ce2b1a6d-e550-0410-aec6-3dcde31c8c00