btrfs: block-group: Rework documentation of check_system_chunk function

Commit 4617ea3a (" Btrfs: fix necessary chunk tree space calculation
when allocating a chunk") removed the is_allocation argument from
check_system_chunk, since the formula for reserving the necessary space
for allocation or removing a chunk would be the same.

So, rework the comment by removing the mention of is_allocation
argument.
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -2987,9 +2987,7 @@ static u64 get_profile_num_devs(struct btrfs_fs_info *fs_info, u64 type)
 }
 
 /*
- * If @is_allocation is true, reserve space in the system space info necessary
- * for allocating a chunk, otherwise if it's false, reserve space necessary for
- * removing a chunk.
+ * Reserve space in the system space for allocating or removing a chunk
  */
 void check_system_chunk(struct btrfs_trans_handle *trans, u64 type)
 {