Remove the old Kerberos 5 authentication code.

Before you complain, this code hasn't seen material change since at least
X11R6.  It certainly does not build with any modern version of Kerberos.
Anybody wanting krb5 auth to their X server should probably be using
GSSAPI instead of internal krb5 API anyway.

include/dixstruct.h

@@ -207,10 +207,6 @@ extern int (* ProcVector[256]) (ClientPtr /*client*/);
 
 extern int (* SwappedProcVector[256]) (ClientPtr /*client*/);
 
-#ifdef K5AUTH
-extern int (*k5_Vector[256])(ClientPtr /*client*/);
-#endif
-
 extern ReplySwapPtr ReplySwapVector[256];
 
 extern int ProcBadRequest(ClientPtr /*client*/);