Remove FLAG_opt_safe_uint32_operations.

It has been turned on by default for a long time, and hydrogenized BinaryOpStubs actually depend on it being turned on.

BUG=v8:3487
LOG=n
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/630023002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24415 ce2b1a6d-e550-0410-aec6-3dcde31c8c00