Keep EnableWebMvcSecurity Link

So that links across the Internet that are pointed at
#mvc-enablewebmvcsecurity still arrive at a relevant place,
this commit re-adds the mvc-enablewebmvcsecurity link, even
though @EnableWebMvcSecurity itself is now removed.

Issue gh-17294

docs/modules/ROOT/pages/servlet/integrations/mvc.adoc

@@ -4,6 +4,7 @@
 Spring Security provides a number of optional integrations with Spring MVC.
 This section covers the integration in further detail.
 
+[[mvc-enablewebmvcsecurity]]
 [[mvc-enablewebsecurity]]
 == @EnableWebSecurity