Remove deprecated containment operators for contrib types.

Remove deprecated containment operators for contrib types.

Since PG 8.2, @ and ~ have been deprecated aliases for the containment
operators @> and <@.  It seems like enough time has passed to actually
remove them, so do so.

This completes the project begun in commit 2f70fdb06.  Note that in
the core types, the relation to the preferred operator names was
reversed from what it is in these contrib modules.  The confusion
that induced was a large part of the reason for deprecation.

Justin Pryzby

Discussion: https://postgr.es/m/20201027032511.GF9241@telsasoft.com