updatecaches: deprecate the `full` argument

Now that all users were migrated, we can use deprecate the old way. This would
give potential extensions code a heads up on the API change.

Differential Revision: https://phab.mercurial-scm.org/D10731

mercurial/localrepo.py

@@ -2754,12 +2754,17 b' class localrepository(object):'
 
         unfi = self.unfiltered()
 
-        if caches is None:
             if full:
+            msg = (
+                "`full` argument for `repo.updatecaches` is deprecated\n"
+                "(use `caches=repository.CACHE_ALL` instead)"
+            )
+            self.ui.deprecwarn(msg, "5.9")
                 caches = repository.CACHES_ALL
                 if full == b"post-clone":
                     caches = repository.CACHES_POST_CLONE
-            else:
+            caches = repository.CACHES_ALL
+        elif caches is None:
                 caches = repository.CACHES_DEFAULT
 
         if repository.CACHE_BRANCHMAP_SERVED in caches: