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

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