psql: Fix tab completion for VACUUM option values

Hi,

I noticed that tab completion for VACUUM option values is broken.
For example, ON or OFF should be suggested after
"VACUUM (VERBOSE", but this currently does not work.

I believe this issue was introduced by commit 8a3e4011, which added
tab completion for the ONLY option of VACUUM and ANALYZE, along with
some code simplification using MatchAnyN.

In addition, tab completion for the ONLY option is insufficient:
"ONLY" is not suggested immediately after a completed option list,
for example in "VACUUM (...) ONLY" or "ANALYZE (...) ONLY".

I've attached a patch to fix these issues.

Regards,
Yugo Nagata

-- 
Yugo Nagata <nagata@sraoss.co.jp>