Add an obsoletion note to our deprecated commands.

Description

As described in #879 (closed) and #881 (closed), our auto-generated documentation and man pages are not coping very well with Click's (relatively new) feature which allows us to hide commands.

This commit is a stop gap solution which explicitly notes that deprecated commands are obsolete in their short help, until the respective upstream issues (which are mentioned in #879 (closed) and #881 (closed)) are addressed.