Remove unneeded argument from Parser::GetSymbol

Parser::GetSymbol can't actually fail, so no need for the bool* ok
argument or the CHECK_OK in callers.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/15421007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14727 ce2b1a6d-e550-0410-aec6-3dcde31c8c00