Remove requirements_style_check

Requirements files should not be kept in alphabetical order, because
pip does not actually have a dep solver. Order is important. This file
should never have existed. While doing this, put pbr at the top of
the file, which is where it needs to be, and remove setuptools_git
which should no longer be used.

Change-Id: I1ae61c1c5ce66ed15fbdefbee063997ea6f3172c
Merge "Remove requirements_style_check"