non-win: Make goma_ctl use vanilla python

This was switched from python to vpython in
https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1962721
for a Windows module. Since vpython doesn't yet work on arm macs, switch
this back to vanilla python on non-win for now.

Bug: 1103236
Change-Id: Id083ad88d8474e283fb9f48d91e343b66aa67e51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2842346
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>

goma_ctl

@@ -9,4 +9,4 @@ MYPATH=$(dirname "${BASH_SOURCE[0]}")
 source "$MYPATH/cipd_bin_setup.sh"
 cipd_bin_setup &> /dev/null
 
-PYTHONDONTWRITEBYTECODE=1 exec vpython "$MYPATH/.cipd_bin/goma_ctl.py" "$@"
+PYTHONDONTWRITEBYTECODE=1 exec python "$MYPATH/.cipd_bin/goma_ctl.py" "$@"