rcu: Remove old debugfs interfaces and also RCU flavor name

This commit removes the old debugfs interfaces, so that the new
directory-per-RCU-flavor versions remain.  Because the RCU flavor is
given by the directory name, there is no need to print it out, so remove
the name from the printout.

Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>