CHROMIUM: Do not explicitly invoke python2_7

python2 is to be deprecated in favor of python3.

BUG=b:181806716
TEST=CQ

Cq-Depend: chrome-internal:3695732
Change-Id: Ic08f31e196b874bf94af63429656ba2e50fa7443
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/edk2/+/3041816
Tested-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Commit-Queue: Tim Wawrzynczak <twawrzynczak@chromium.org>