This reverts commit e44595f2.
Reason for revert: build/mac_toolchain.py still fails with my local Python 3.9. Let's not make this change until the top level Chromium DEPS file does.
Original change's description:
> Update DEP actions for Python 3
>
> build/mac_toolchain.py was fixed for Python 3 in
> https://crrev.com/c/2727724
>
> Bug: angleproject:5707
> Change-Id: I2f233157bedc3cc298250b8efc9bd68ac45cdc28
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2731707
> Reviewed-by: Jamie Madill <jmadill@chromium.org>
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
Bug: angleproject:5707
Change-Id: Ib955a6343d886d273d7e949815fba5366b169386
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2753335
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
