This reverts commit dbca865e.

Reason for revert:

Fails on Mac

$ gclient sync --with_branch_heads
awk: syntax error at source line 1
 context is
	match($0, >>>  /cpython3\/.*version:([.0-9a-zA-Z]+)/, <<<
awk: bailing out at source line 1
Could not extract Python 3 version from manifest.


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>

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

Change-Id: I8e03a9e22655491d0f8e8d214d04ba749c2ab8ab
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1002153
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1797197Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>