docs: random: Use past tense as this backend is long gone

For an event that happend at a definite time in the past, past simple is
the right tense.

Suggested-by: Josh Soref (josref)

docs/backends/random.rst

@@ -2,7 +2,7 @@ Random Backend
 ==============
 
 .. deprecated:: 4.6.0
-  This backend has been removed in 4.6.0
+  This backend was removed in 4.6.0
 
 * Native: Yes
 * Primary: No
@@ -20,14 +20,14 @@ Random Backend
 * Module name: random
 * Launch: ``random``
 
-This is a very silly backend which is discussed in the :doc:`Backends
-writer's guide <../appendices/backend-writers-guide>`.
-as a demonstration on how to write a PowerDNS backend.
+This used to be a very silly backend which is still discussed in the
+:doc:`Backends writer's guide <../appendices/backend-writers-guide>`.  as a
+demonstration on how to write a PowerDNS backend.
 
-This backend knows about only one hostname, and only about its IP
-address at that. With every query, a new random IP address is generated.
+This backend knew about only one hostname, and only about its IP
+address at that. With every query, a new random IP address was generated.
 
-It only makes sense to load the random backend in combination with a
+It only made sense to load the random backend in combination with a
 regular backend. This can be done by prepending it to the
 :ref:`setting-launch` instruction, such as
 ``launch=random,gmysql``.