remove --namespace-packages from pre-commit

.pre-commit-config.yaml

     -   id: mypy
         name: mypy-ml-agents
         files: "ml-agents/.*"
-        args: [--ignore-missing-imports, --disallow-incomplete-defs, --namespace-packages]
+        args: [--ignore-missing-imports, --disallow-incomplete-defs]
-        args: [--ignore-missing-imports, --disallow-incomplete-defs,  --namespace-packages]
+        args: [--ignore-missing-imports, --disallow-incomplete-defs]
-        args: [--ignore-missing-imports, --disallow-incomplete-defs,  --namespace-packages]
+        args: [--ignore-missing-imports, --disallow-incomplete-defs]
 
 -   repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v2.4.0