btrfs: delete stale comments after merge conflict resolution

There are two comments in btrfs_cache_block_group that I left when
resolving conflict between commits ced8ecf0 "btrfs: fix space cache
corruption and potential double allocations" and 527c490f "btrfs:
delete btrfs_wait_space_cache_v1_finished".

The former reworked the caching logic to wait until the caching ends in
btrfs_cache_block_group while the latter only open coded the waiting.
Both removed btrfs_wait_space_cache_v1_finished, the correct code is
with the waiting and returning error. Thus the conflict resolution was
OK.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -774,10 +774,8 @@ int btrfs_cache_block_group(struct btrfs_block_group *cache, bool wait)
 
 	btrfs_queue_work(fs_info->caching_workers, &caching_ctl->work);
 out:
-	/* REVIEW */
 	if (wait && caching_ctl)
 		ret = btrfs_caching_ctl_wait_done(cache, caching_ctl);
-		/* wait_event(caching_ctl->wait, space_cache_v1_done(cache)); */
 	if (caching_ctl)
 		btrfs_put_caching_control(caching_ctl);