Remove unnecessary git completion file
.osx: Add back the “increase window resize speed” hack

It didn’t work in OS X 10.10 anymore, but it seems OS X 10.10.1 does support it.

Ref. 4471e2732faede1d9b242cb547de8005578b3d10.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  .osx: Add back the “increase window resize speed” hack