Summary:
This removes Cython as a build dependency as requested by our users.
Added a test to prevent check-in files with `/home/`.
Modified check-code to skip checking Cython generated files.
Test Plan:
Run `make clean local` with Cython installed and uninstalled.
Also run `make clean local` with `USECYTHON=1` and `0`.
Reviewers: #mercurial, mitrandir
Reviewed By: mitrandir
Subscribers: mjpieters, medson
Differential Revision: https://phabricator.intern.facebook.com/D5252935
Signature: t1:5252935:1497525190:402798077d44e39e24fcb037535ec7ffd1af9c4b