debugdiscovery: correct and clean up command synopsis

This does a few things:

 * Changes "-r" to "--rev", since "-r" is not a valid short form
 * Removes non-existent "-l" and "-b" options
 * Removes "..." after options, since we don't usually have that

Differential Revision: https://phab.mercurial-scm.org/D1706

mercurial/debugcommands.py

@@ -740,7 +740,7 b' def debugstate(ui, repo, **opts):'
      _('use old-style discovery with non-heads included')),
     ('', 'rev', [], 'restrict discovery to this set of revs'),
     ] + cmdutil.remoteopts,
-    _('[-l REV] [-r REV] [-b BRANCH]... [OTHER]'))
+    _('[--rev REV] [OTHER]'))
 def debugdiscovery(ui, repo, remoteurl="default", **opts):
     """runs the changeset discovery protocol in isolation"""
     opts = pycompat.byteskwargs(opts)