btrfs: remove hole check in prealloc_file_extent_cluster

Extents in the extent cluster are guaranteed to be contiguous as such
the hole check inside the loop can never trigger. In fact this check was
never functional since it was added in 1851309 ("btrfs: update
btrfs_space_info's bytes_may_use timely") which came after the commit
introducing clustered/contiguous extents 0257bb8 ("Btrfs: relocate
file extents in clusters").

Let's just remove it as it adds noise to the source.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -2604,9 +2604,6 @@ int prealloc_file_extent_cluster(struct inode *inode,
 
 		lock_extent(&BTRFS_I(inode)->io_tree, start, end);
 		num_bytes = end + 1 - start;
-		if (cur_offset < start)
-			btrfs_free_reserved_data_space_noquota(inode,
-						       start - cur_offset);
 		ret = btrfs_prealloc_file_range(inode, 0, start,
 						num_bytes, num_bytes,
 						end + 1, &alloc_hint);