Fixed code misc. quality issues (#9649)

- Merge 'isinstance' calls.
- Remove unnecessary dict call outside of comprehension.
- Use 'sys.exit()' calls.

synapse/push/httppusher.py

@@ -290,7 +290,7 @@ class HttpPusher(Pusher):
         if rejected is False:
             return False
 
-        if isinstance(rejected, list) or isinstance(rejected, tuple):
+        if isinstance(rejected, (list, tuple)):
             for pk in rejected:
                 if pk != self.pushkey:
                     # for sanity, we only remove the pushkey if it

synapse/util/frozenutils.py

@@ -36,7 +36,7 @@ def freeze(o):
 
 def unfreeze(o):
     if isinstance(o, (dict, frozendict)):
-        return dict({k: unfreeze(v) for k, v in o.items()})
+        return {k: unfreeze(v) for k, v in o.items()}
 
     if isinstance(o, (bytes, str)):
         return o