This reverts commits 0e85f633 and 9d25ad41.

Reason for revert:

Causes problems for MinGW users.

Original change's description:
> Reland "depot_tools: Bootstrap Python 3 on Linux/Mac"
>
> This is a reland of dbca865e
>
> Original change's description:
> > depot_tools: Bootstrap Python 3 on Linux/Mac
> >
> > This will make it possible for developers to execute depot_tools
> > scripts using Python 3 in a known environment.
> >
> > Bug: 1002153
> > Change-Id: I5ff492a49d227c1b5876f49adba020f51a575bdd
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1762664
> > Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
> > Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> > Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
>
> Bug: 1002153
> Change-Id: I6938a76ffa05366c21f7c56aed3d07ecb2b84443
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1798845
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

TBR=iannucci@chromium.org,dpranke@chromium.org,tandrii@google.com,ehmaldonado@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1002153
Change-Id: I3ee87b95b2532ec694d7f4f87cce8cde8ccf86eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1808137Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>