Cleanup GaussianFlux test, use more test utility code
Remove relic code from GaussianFlux

This looks like a combination of copy/paste relics from PsfFlux, as well
as some config options that should have been removed in DM-1015, when we
stopped having a use for them.
Bail out early if one of a plugin's dependencies failed

This currently only applies to shapes, because we fall back to using the Peak
when a centroid measurement fails.
Add aliases to flags of dependencies in dependent algorithms.
Add test for shape dependency error handling in GaussianFlux