vacuumdb: Do not run VACUUM (ONLY_DATABASE_STATS) when --analyze-only.

vacuumdb: Do not run VACUUM (ONLY_DATABASE_STATS) when --analyze-only.

Previously, vacuumdb --analyze-only issued VACUUM (ONLY_DATABASE_STATS)
at the end. Since --analyze-only is meant to update optimizer statistics only,
this extra VACUUM command is unnecessary.

This commit prevents vacuumdb --analyze-only from running that redundant
VACUUM command.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Mircea Cadariu <cadariu.mircea@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwEqHGa-k=wbRMucUVihHVXk4NQkK94GNN=ym9cQ5HBSHg@mail.gmail.com