reindexdb: Allow specifying objects to process in all databases.

reindexdb: Allow specifying objects to process in all databases.

Presently, reindexdb's --table, --schema, --index, and --system
options cannot be used together with --all, i.e., you cannot
specify objects to process in all databases.  This commit removes
this unnecessary restriction.  Furthermore, it removes the
restriction that --system cannot be used with --table, --schema,
and --index.  There is no such restriction for the latter options,
and there is no technical reason to disallow these combinations.

Reviewed-by: Kyotaro Horiguchi, Dean Rasheed
Discussion: https://postgr.es/m/20230628232402.GA1954626%40nathanxps13