Unregister aliases when a datastore option is unregistered

[busterb]

Per #10981 (comment) if you unregister a datastore option with an alias, the alias would continue existing after the original option, causing it to continue receiving assignment values. The alias would continue overshadowing any directly-registered options as well.

This fixes 'delete' in the datastore class so it removes aliases for the deleted option. It also modifies find_key_case to require that an alias key actually exist before returning it (belt-and-suspenders), and observes that the linear scan of all keys was pointless in the non-alias case, since we fall through to returning the key anyway on no match.

Verification Steps

• modify the module referenced in start printjob docs and bug fixes #10981 and deregister the 'RHOSTS' option
• verify that you can still set 'rhost' and 'RHOST' and the actual datastore option is updated

[acammack-r7]

Release Notes

When unregistering options for a module, aliases are now also unregistered. To avoid option name conflicts, the list of available options is now checked before the list of aliases.