rcu: Remove CONFIG_PREEMPT_RCU

Now that CONFIG_TREE_PREEMPT_RCU is in place, there is no
further need for CONFIG_PREEMPT_RCU.  Remove it, along with
whatever subtle bugs it may (or may not) contain.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
LKML-Reference: <125097461396-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f87fb0c..82fbc49 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -725,7 +725,7 @@
 
 config RCU_CPU_STALL_DETECTOR
 	bool "Check for stalled CPUs delaying RCU grace periods"
-	depends on CLASSIC_RCU || TREE_RCU || TREE_PREEMPT_RCU
+	depends on TREE_RCU || TREE_PREEMPT_RCU
 	default n
 	help
 	  This option causes RCU to printk information on which