doc: Remove references to arrayRCU.rst

arrayRCU.rst has been removed since commit ef2555cf ("doc: Remove
arrayRCU.rst") but is still referenced by whatisRCU.rst. Update it to
reflect the current state of the documentation.
Signed-off-by: Zenghui Yu <zenghui.yu@linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Documentation/RCU/whatisRCU.rst

@@ -427,7 +427,7 @@ their assorted primitives.
 
 This section shows a simple use of the core RCU API to protect a
 global pointer to a dynamically allocated structure.  More-typical
-uses of RCU may be found in listRCU.rst, arrayRCU.rst, and NMI-RCU.rst.
+uses of RCU may be found in listRCU.rst and NMI-RCU.rst.
 ::
 
 	struct foo {
@@ -510,8 +510,8 @@ So, to sum up:
 	data item.
 
 See checklist.rst for additional rules to follow when using RCU.
-And again, more-typical uses of RCU may be found in listRCU.rst,
-arrayRCU.rst, and NMI-RCU.rst.
+And again, more-typical uses of RCU may be found in listRCU.rst
+and NMI-RCU.rst.
 
 .. _4_whatisRCU: