pgsql: Update heap_page_prune() free space map comments.

Update heap_page_prune() free space map comments.

It is up to the heap_page_prune() caller to decide what to do about
updating the FSM for a page following pruning.  Update old comments that
address what we might want to do as if it was the responsibility of
heap_page_prune() itself.  heap_page_prune() doesn't have enough
high-level context to make a sensible choice.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/42f9427aa98a2245d29737e0f3b8aaf39a7f57ec

Modified Files
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src/backend/access/heap/pruneheap.c | 25 ++++++++-----------------
1 file changed, 8 insertions(+), 17 deletions(-)