bundle2: use discard to remove bundle2 cap

caps.remove('bundle2') was throwing an exception if bundle2 wasn't present in
the capabilities. This was causing test-static-http.t to hang. Let's just use
discard, so we don't get an exception.

mercurial/localrepo.py

@@ -281,7 +281,7 b' class localrepository(object):'
         # required by the tests (or some brave tester)
         if not self.ui.configbool('server', 'bundle2', False):
             caps = set(caps)
-            caps.remove('bundle2')
+            caps.discard('bundle2')
         return caps
 
     def _applyrequirements(self, requirements):