In commit fd26a880 we added a worst case estimate for rmapbt blocks
needed to satisfy the block mapping request.  Since then, we added the
ability to reserve enough space in each AG such that we should never run
out of blocks to grow the rmapbt, which makes this calculation
unnecessary.  Revert the commit because it makes the extra delalloc
indlen accounting unnecessary and incorrect.
Reported-by: NEryu Guan <eguan@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>