post-3085 cleanup

After merging https://dev.lsstcorp.org/trac/ticket/3085 from LSST, we can remove an ugly workaround in the HSC forced photometry code.  This includes an HSC-specific butler argument to `getSchemaCatalogs()` in pipe_base, which this PR removes, bringing the HSC base closer to the LSST version.

See also the PR in pipe_tasks.

I'd merge this myself, but I'd prefer to wait until the integration tester is up and running again just in case I've made a stupid mistake.