remove gevent/core.c

the releases will continue to include it but it no longer useful to keep it in the repo as it's much easier to build now, setup.py will do that automatically.

--HG--
extra : transplant_source : %F7%DF%3E%D3%C1t%82.X%9F%CD%C2F%E4%DE%60%A4%7F%E1h