pgsql: Fix memory leak introduced in commit 7df159a620.

Fix memory leak introduced in commit 7df159a620.

We memorize all internal and empty leaf pages in the 1st vacuum stage for
gist indexes.  They are used in the 2nd stage, to delete all the empty
pages.  There was a memory context page_set_context for this purpose, but
we never used it.

Reported-by: Amit Kapila
Author: Dilip Kumar
Reviewed-by: Amit Kapila
Backpatch-through: 12, where it got introduced
Discussion: https://postgr.es/m/CAA4eK1LGr+MN0xHZpJ2dfS8QNQ1a_aROKowZB+MPNep8FVtwAA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/70a6c37d524cc2c29712424785be3d9e2e62f484

Modified Files
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src/backend/access/gist/gistvacuum.c | 10 ++++++++++
1 file changed, 10 insertions(+)