Remove new_semantic_analyzer from config parameters (#7529)

Fixes #7523.

Author: onlined

mypy/config_parser.py

@@ -178,7 +178,12 @@ def parse_section(prefix: str, template: Options,
         if key in config_types:
             ct = config_types[key]
         else:
-            dv = getattr(template, key, None)
+            dv = None
+            # We have to keep new_semantic_analyzer in Options
+            # for plugin compatibility but it is not a valid option anymore.
+            assert hasattr(template, 'new_semantic_analyzer')
+            if key != 'new_semantic_analyzer':
+                dv = getattr(template, key, None)
             if dv is None:
                 if key.endswith('_report'):
                     report_type = key[:-7].replace('_', '-')