[arm] Drop useless branches in full and lithium codegen.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/100483006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18429 ce2b1a6d-e550-0410-aec6-3dcde31c8c00