Remove unique static RegExpEmpty instance.

R=marja@chromium.org
BUG=chromium:430652
LOG=N

Review URL: https://codereview.chromium.org/716113002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25284 ce2b1a6d-e550-0410-aec6-3dcde31c8c00