subrepo: drop the 'ui' parameter to cat()

This no longer needs to be explicitly passed because the subrepo object tracks
a 'ui' reference since fcbc66b5da6a.  See the change to 'archive' for details
about the differences between the output level in the root repo and subrepo 'ui'
object.

The only use for 'ui' in cat is to emit a status message when a subrepo is
missing.  The bad() method on the matcher still uses the root repo's ui, because
narrowing the matcher doesn't change the ui object.

mercurial/cmdutil.py

@@ -2182,7 +2182,7 b' def cat(ui, repo, ctx, matcher, prefix, '
         try:
             submatch = matchmod.narrowmatcher(subpath, matcher)
 
-            if not sub.cat(ui, submatch, os.path.join(prefix, sub._path),
+            if not sub.cat(submatch, os.path.join(prefix, sub._path),
                            **opts):
                 err = 0
         except error.RepoLookupError:

mercurial/subrepo.py

@@ -442,7 +442,7 b' class abstractsubrepo(object):'
         self.ui.warn("%s: %s" % (prefix, _("addremove is not supported")))
         return 1
 
-    def cat(self, ui, match, prefix, **opts):
+    def cat(self, match, prefix, **opts):
         return 1
 
     def status(self, rev2, **opts):
@@ -636,10 +636,10 b' class hgsubrepo(abstractsubrepo):'
                                  dry_run, similarity)
 
     @annotatesubrepoerror
-    def cat(self, ui, match, prefix, **opts):
+    def cat(self, match, prefix, **opts):
         rev = self._state[1]
         ctx = self._repo[rev]
-        return cmdutil.cat(ui, self._repo, ctx, match, prefix, **opts)
+        return cmdutil.cat(self.ui, self._repo, ctx, match, prefix, **opts)
 
     @annotatesubrepoerror
     def status(self, rev2, **opts):