gfs2: don't lock sd_log_flush_lock in try_rgrp_unlink
In function try_rgrp_unlink, we added a temporary lock of the
sd_log_flush_lock while searching the bitmaps. This protected us from
problems in which dinodes being freed were still in a state of flux
because the rgrp was in an active transaction. It was a kludge.
Now that we've straightened out the code for inode eviction, deletes,
and all the recovery mess, we no longer need this kludge.
This patch removes it, and should improve performance.