Get rid of the binop_stub parameter to BuildBinaryOperation().

Just ask the graph builder whether we are compiling a stub.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/83073003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18004 ce2b1a6d-e550-0410-aec6-3dcde31c8c00