btrfs: qgroup: delete a TODO about using kmem cache to allocate structures

Generic slab works fine allocating btrfs_qgroup_extent_record
structures. It's not necessary to create a dedicated kmem cache that
would be created but unused if quotas were not enabled. Let's delete the
TODO line.

Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: Junchao Sun <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: jc2870

fs/btrfs/qgroup.h

@@ -123,7 +123,6 @@ struct btrfs_inode;
 
 /*
  * Record a dirty extent, and info qgroup to update quota on it
- * TODO: Use kmem cache to alloc it.
  */
 struct btrfs_qgroup_extent_record {
 	struct rb_node node;