Revert of Attempt to fix expansion of the goma directory in MB on windows. (patchset...

Revert of Attempt to fix expansion of the goma directory in MB on windows. (patchset #3 id:40001 of https://codereview.chromium.org/1356743002/ )

Reason for revert:
this did not actually fix things and so I'm reverting it to work on a proper solution

Original issue's description:
> Attempt to fix expansion of the goma directory in MB on windows.
>
> It looks like backslashes are not being escaped correctly, and
> so we're getting an invalid path to the goma toolchain when
> trying to build.
>
> R=scottmg@chromium.org
> NOTRY=true
> BUG=
>
> Committed: https://crrev.com/d4899050a97ed035707b75cd884ac9ebcb5e8206
> Cr-Commit-Position: refs/heads/master@{#349529}

TBR=scottmg@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1348923005

Cr-Commit-Position: refs/heads/master@{#349538}