Clarify rooms.md

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

docs/admin_api/rooms.md

@@ -546,7 +546,7 @@ A response as follows will be returned:
 
 ## Deleting forward extremities
 
-In the event a room has lots of forward extremities, the extra can be
+If a room has lots of forward extremities, the extra can be
 deleted as follows:
 
 ```