rcutorture: Remove TREE06 and TREE08 from the default test list

Now that there is only one RCU flavor to rule them all, the TREE06
and TREE08 test scenarios are redundant.  This commit therefore removes
them.  Later changes will rebalance and renumber the tests.

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

tools/testing/selftests/rcutorture/configs/rcu/CFLIST

@@ -3,9 +3,7 @@ TREE02
 TREE03
 TREE04
 TREE05
-TREE06
 TREE07
-TREE08
 TREE09
 SRCU-N
 SRCU-P