Clean up useless "skipping" messages for VACUUM/ANALYZE.
When VACUUM/ANALYZE are run on an entire database, it warns of
skipping relations for which the user doesn't have sufficient
privileges. That only makes sense for tables, so skip such messages
for indexes, etc.
Reviewed-by: Nathan Bossart
Discussion: https://postgr.es/m/
c0a85c2e83158560314b576b6241c8ed0aea1745.camel%40j-davis.com