Set up regression-test .cfg file so it will be picked up

A couple of changes:

 - The name: should just be 'regression-test.cfg'
 - The comments: not from DocStrip so remove those parts (might otherwise
   be misleading)


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5131 de43f980-851b-0410-b2f7-c40aca1f87e0
l3build: Use DocStrip version of regression-test, etc.

This removes the need to have a copy of regression-test.tex in support.
At the same time, as the 'standard' position is that nothing is run in isolation
it does not make sense to copy any support files. Instead, do this just for
our own code, and be selective about waht we copy (presumably the best plan).


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5132 de43f980-851b-0410-b2f7-c40aca1f87e0