pgsql: Remove open-coding of index_set_state_flags

Remove open-coding of index_set_state_flags

(The new code does reset indisclustered and indisreplident in addition
to indisvalid, but that doesn't harm anything as far as I can tell.)

I (Álvaro) failed to notice I was writing duplicate code for commit
8b08f7d4820f.

Extracted from a larger patch by the same author.

Author: Justin Pryzby <pryzbyj(at)telsasoft(dot)com>
Reviewed-by: Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>
Discussion: https://postgr.es/m/20201031063117.GF3080@telsasoft.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2b4b768537f39ab5ebc31548829889a0bf2e4395

Modified Files
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src/backend/commands/indexcmds.c | 16 +---------------
1 file changed, 1 insertion(+), 15 deletions(-)