xfs: only check mergeability of bnobt records

xfs: only check mergeability of bnobt records

In the cntbt (free space by block count) btree, records are not supposed
to be in startblock order.  Hence the mergeability check is pointless.
Remove it, since it does nothing, as LOLLM points out.

Cc: stable@vger.kernel.org # v6.4
Fixes: d5784ae82778d9 ("xfs: flag free space btree records that could be merged")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>