ARM: replace RegExpCEntryStub with DirectCEntryStub.

RegExpCEntryStub is therefore removed.

BUG=none
TEST=none
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/23468015

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16618 ce2b1a6d-e550-0410-aec6-3dcde31c8c00