Fix HGraphBuilder::AddSimulate to pass removable down correctly

It was passed as a position argument previously making all simulates added with it conservatively FIXED_SIMULATE.

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/146013002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18822 ce2b1a6d-e550-0410-aec6-3dcde31c8c00