logging: Use django.server to filter 200 and 304.

Previously, we were monkey patching the runserver command
in zerver/management/commands/rundjango.py for this.

zerver/lib/logging_util.py

@@ -61,3 +61,13 @@ class RequireReallyDeployed(logging.Filter):
         # type: (logging.LogRecord) -> bool
         from django.conf import settings
         return settings.PRODUCTION
+
+def skip_200_and_304(record):
+    # type: (logging.LogRecord) -> bool
+    # Apparently, `status_code` is added by Django and is not an actual
+    # attribute of LogRecord; as a result, mypy throws an error if we
+    # access the `status_code` attribute directly.
+    if getattr(record, 'status_code') in [200, 304]:
+        return False
+
+    return True