Remove [[PROTOTYPE]] from ObjectToStringHarmony

harmony-tostring needs to emulate InstallFunctions --- InstallFunctions will fail
in Debug builds because the `toString` property already exists in Object.prototype.

The fix is to add some of the other features from InstallFunctions() to the
setup of ObjectToStringHarmony.

R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/667263004

Patch from Caitlin Potter <caitpotter88@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24808 ce2b1a6d-e550-0410-aec6-3dcde31c8c00