Use rbc_dashboard.py instead of rbc_regression_test.sh

rbc_dashboard.py is an alternative implementation of
rbc_regression_test.sh. These tests both run soong 2 times with
starlark product config enabled/disabled and diff the resulting ninja
files. However, the shell script test runs the soong invications in
series and the python one runs them in parallel, meaning the python
one is faster. On my computer the shell one takes ~7 minutes and the
python one takes ~4 minutes.

Bug: 291548757
Test: Presubmits
Change-Id: I20fd6ca09f47dd0547f2681fbd78ba70991493b0