Revert of Generalize python_git_runner for use in non-git scripts.

Revert of Generalize python_git_runner for use in non-git scripts. (patchset #1 id:1 of https://codereview.chromium.org/1415993003/ )

Reason for revert:
Speculative revert in case this caused the bots to fail bot_update.

Original issue's description:
> Generalize python_git_runner for use in non-git scripts.
> 
> Also fixes an msys (git-bash) incompatibility, similar to the one
> fixed in crrev.com/4845f0ed694ff071da5f6ee937a0bce2ea4e6fd2.
> 
> This change doesn't actually use the wrapper in any new places, but
> subsequent changes will be made to use it in places where
> 'exec python' is called directly, like gclient and fetch.
> 
> BUG=411518
> R=iannucci@google.com
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=297357

TBR=iannucci@google.com,iannucci@chromium.org,mmoss@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=411518
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=297358

[Adrian Kuegel, 2015-10-28 15:41:03]

Created Revert of Generalize python_git_runner for use in non-git scripts.

[commit-bot: I haz the power, 2015-10-28 15:41:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1414923008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1414923008/1

[commit-bot: I haz the power, 2015-10-28 15:41:26]

Committed patchset #1 (id:1) as
http://src.chromium.org/viewvc/chrome?view=rev&revision=297358