xen/arm64: Drop relocate_and_switch_ttbr() stub

In the original patch e7a80636f1 ("xen/arm: add cache coloring support
for Xen image"), the stub was added under wrong assumption that DCE
won't remove the function call if it's not static. This assumption is
incorrect as we already rely on DCE for cases like this one. Therefore
drop the stub, that otherwise would be a place potentially prone to
errors in the future.

Suggested-by: Julien Grall <julien@xen.org>
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

xen/arch/arm/arm64/mmu/mm.c

@@ -171,8 +171,6 @@ void __init relocate_and_switch_ttbr(uint64_t ttbr)
      */
     update_identity_mapping(false);
 }
-#else
-void __init relocate_and_switch_ttbr(uint64_t ttbr) {}
 #endif
 
 void __init switch_ttbr(uint64_t ttbr)