Fix mypy violations (for mypy-0.761)

Author: tk0miya

setup.py

@@ -47,7 +47,7 @@
         'html5lib',
         'flake8>=3.5.0',
         'flake8-import-order',
-        'mypy>=0.750',
+        'mypy>=0.761',
         'docutils-stubs',
     ],
 }

sphinx/pycode/parser.py

@@ -129,7 +129,7 @@ class TokenProcessor:
     def __init__(self, buffers: List[str]) -> None:
         lines = iter(buffers)
         self.buffers = buffers
-        self.tokens = tokenize.generate_tokens(lambda: next(lines))  # type: ignore
+        self.tokens = tokenize.generate_tokens(lambda: next(lines))
         self.current = None     # type: Token
         self.previous = None    # type: Token