tags: no need to check for valid nodes

_findtags in localrepo checks that nodes exist in the revlog so we
can't get a LookupError here.

The output of 'hg tags' stays the same since tags to unknown nodes
didn't get printed before anyway due to ae3089cefaab.

mercurial/commands.py

@@ -4061,13 +4061,10 def tags(ui, repo):
             ui.write("%s\n" % t)
             continue
 
-        try:
             hn = hexfunc(n)
             r = "%5d:%s" % (repo.changelog.rev(n), hn)
-        except error.LookupError:
-            r = "    ?:%s" % hn
-        else:
             spaces = " " * (30 - encoding.colwidth(t))
+
             if ui.verbose:
                 if repo.tagtype(t) == 'local':
                     tagtype = " local"