Remove Byte Order Mark from git/cmd.py

The Unicode Byte Order Mark is usually unwanted. git/cmd.py had one
inserted in 2008 by cf37099e, a commit that fix a Windows related issue
which indicate the file has most probably be edited with a text editor
that automatically insert the Byte Order Mark.

Remove the BOM from git/cmd.py

For details aboute the BOM:
    https://en.wikipedia.org/wiki/Byte_order_mark