percpu-rwsem: kill CONFIG_PERCPU_RWSEM

Remove CONFIG_PERCPU_RWSEM, the next patch adds the unconditional
user of percpu_rw_semaphore.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

init/Kconfig

@@ -925,7 +925,6 @@ config NUMA_BALANCING_DEFAULT_ENABLED
 menuconfig CGROUPS
 	bool "Control Group support"
 	select KERNFS
-	select PERCPU_RWSEM
 	help
 	  This option adds support for grouping sets of processes together, for
 	  use with process control subsystems such as Cpusets, CFS, memory