Revert "GeneratorFunction() makes generator instances"

This reverts r14684 because of blink LayoutTest failures in
inspector/debugger/debugger-pause-in-internal.html.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/14619040

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14694 ce2b1a6d-e550-0410-aec6-3dcde31c8c00