btrfs: remove useless comments

Fixes: ("btrfs: update btrfs_space_info's bytes_may_use timely")

Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -6499,16 +6499,9 @@ void btrfs_wait_block_group_reservations(struct btrfs_block_group_cache *bg)
  * @num_bytes:	The number of bytes in question
  * @delalloc:   The blocks are allocated for the delalloc write
  *
- * This is called by the allocator when it reserves space. Metadata
- * reservations should be called with RESERVE_ALLOC so we do the proper
- * ENOSPC accounting.  For data we handle the reservation through clearing the
- * delalloc bits in the io_tree.  We have to do this since we could end up
- * allocating less disk space for the amount of data we have reserved in the
- * case of compression.
- *
- * If this is a reservation and the block group has become read only we cannot
- * make the reservation and return -EAGAIN, otherwise this function always
- * succeeds.
+ * This is called by the allocator when it reserves space. If this is a
+ * reservation and the block group has become read only we cannot make the
+ * reservation and return -EAGAIN, otherwise this function always succeeds.
  */
 static int btrfs_add_reserved_bytes(struct btrfs_block_group_cache *cache,
 				    u64 ram_bytes, u64 num_bytes, int delalloc)