pgsql: Improve comments in vacuum_rel() and analyze_rel().

Improve comments in vacuum_rel() and analyze_rel().

Remove obsolete references to get_rel_oids(). Avoid listing specific
relkinds in the comments, since we seem unable to keep such things
in sync with the code, and it's not all that helpful anyhow.

Noted by Michael Paquier, though I rewrote the comments a bit more.

Discussion: https://postgr.es/m/CAB7nPqTWiN9zwKTaOrsnKiGDChqRt7C1+CiiDk4N4OMn92rs6A@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4d85c2900b113e331925baf308cc7fc75ac4530b

Modified Files
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src/backend/commands/analyze.c | 4 +---
src/backend/commands/vacuum.c | 16 ++++++++--------
2 files changed, 9 insertions(+), 11 deletions(-)