[mesa] python_exec.py -> python_exec.sh

Same functionality, less work.

Ran into this while playing with fxr/437319. I think the hop through
python_exec.py was messing with filesystem tracing somehow.
Anyway, I think this is strictly an improvement regardless of the
circumstances. :)

Change-Id: If5b67c0368f1b0b1c898dba1cecf45dbe2ea2584
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/437895
Reviewed-by: Craig Stout <cstout@google.com>
7 files changed