pgsql: Remove unused code for unlogged materialized views.

Remove unused code for unlogged materialized views.

Commit 3bf3ab8c56 initially introduced support for unlogged
materialized views, but this was later disallowed by commit 3223b25ff7.
Additionally, commit d25f519107 added more code for handling
unlogged materialized views. This commit cleans up all unused
code related to them.

If unlogged materialized views had been supported in any official
release, psql would need to retain code to handle them for compatibility
with older servers. However, since they were never included in
an official release, this code is no longer necessary.

Author: Pixian Shi
Reviewed-by: Yugo Nagata, Fujii Masao
Discussion: https://postgr.es/m/CAAccyYKRZ=OvAvgowiSH+OELbStLP=p2Ht=R3CgT=OaNSH5DAA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9272bdeac879ae44907422dd545f8d767b39c5ad

Modified Files
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src/backend/access/heap/heapam_handler.c | 1 -
src/bin/psql/describe.c | 8 ++------
2 files changed, 2 insertions(+), 7 deletions(-)