GitLab

This has been deprecated and replaced by the NodeBuilder system
for a good while now; time to scrape it into the dustbin completely.

Tests that were primarily on the mutable node system itself also
drop, so, this is a *very* large delete diff.

A few other tests used MutableNode just incidentally, and those are
quick fixed to use NodeBuilder.
Signed-off-by: Eric Myhre <hash@exultant.us>