fs: remove comment about d_rcu_to_refcount

This function no longer exists.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20240802-openfast-v1-1-a1cff2a33063@kernel.orgSigned-off-by: Christian Brauner <brauner@kernel.org>

fs/dcache.c

@@ -2163,9 +2163,6 @@ static noinline struct dentry *__d_lookup_rcu_op_compare(
  * without taking d_lock and checking d_seq sequence count against @seq
  * returned here.
  *
- * A refcount may be taken on the found dentry with the d_rcu_to_refcount
- * function.
- *
  * Alternatively, __d_lookup_rcu may be called again to look up the child of
  * the returned dentry, so long as its parent's seqlock is checked after the
  * child is looked up. Thus, an interlocking stepping of sequence lock checks