Move utils out of React that aren't being used

Many of React's util functions are non-redundant with Facebook's core
libraries, so move them out of React into a central location (out of
this repo).

These files were not getting used by any part of React core, so didn't
actually belong here anyway.
Sync modules to vendor/core

We haven't done this recently. Nothing has changed significantly, though
this does remove some files we weren't using.