fs/Kconfig: kill CONFIG_PERCPU_RWSEM some more

As of commit bf3eac8 ("percpu-rwsem: kill CONFIG_PERCPU_RWSEM") we
unconditionally build pcpu-rwsems.  Remove a leftover in for
FILE_LOCKING.

Link: http://lkml.kernel.org/r/20170518180115.2794-1-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/Kconfig

@@ -80,7 +80,6 @@ config EXPORTFS_BLOCK_OPS
 config FILE_LOCKING
 	bool "Enable POSIX file locking API" if EXPERT
 	default y
-	select PERCPU_RWSEM
 	help
 	  This option enables standard file locking support, required
           for filesystems like NFS and for the flock() system