Switch usages of mypy_extensions.NoReturn over to typing.NoReturn. (#1942)

* Change mypy_extensions.NoReturn to typing.NoReturn everywhere.

stdlib/3/_dummy_thread.pyi

@@ -1,5 +1,4 @@
-from mypy_extensions import NoReturn
-from typing import Any, Callable, Dict, Optional, Tuple
+from typing import Any, Callable, Dict, NoReturn, Optional, Tuple
 
 TIMEOUT_MAX: int
 error = RuntimeError

stdlib/3/builtins.pyi

@@ -2,7 +2,7 @@
 
 from typing import (
     TypeVar, Iterator, Iterable, overload, Container,
-    Sequence, MutableSequence, Mapping, MutableMapping, Tuple, List, Any, Dict, Callable, Generic,
+    Sequence, MutableSequence, Mapping, MutableMapping, NoReturn, Tuple, List, Any, Dict, Callable, Generic,
     Set, AbstractSet, FrozenSet, MutableSet, Sized, Reversible, SupportsInt, SupportsFloat,
     SupportsBytes, SupportsAbs, SupportsRound, IO, Union, ItemsView, KeysView, ValuesView,
     ByteString, Optional, AnyStr, Type,
@@ -10,7 +10,6 @@ from typing import (
 from abc import abstractmethod, ABCMeta
 from types import TracebackType, CodeType
 import sys
-from mypy_extensions import NoReturn
 
 # Note that names imported above are not automatically made visible via the
 # implicit builtins import.

stdlib/3/os/__init__.pyi

@@ -4,10 +4,9 @@
 from io import TextIOWrapper as _TextIOWrapper
 import sys
 from typing import (
-    Mapping, MutableMapping, Dict, List, Any, Tuple, IO, Iterable, Iterator, overload, Union, AnyStr,
+    Mapping, MutableMapping, Dict, List, Any, Tuple, IO, Iterable, Iterator, NoReturn, overload, Union, AnyStr,
     Optional, Generic, Set, Callable, Text, Sequence, NamedTuple, TypeVar, ContextManager
 )
-from mypy_extensions import NoReturn
 
 # Re-exported names from other modules.
 from builtins import OSError as error

stdlib/3/sys.pyi

@@ -4,12 +4,11 @@
 # based on http://docs.python.org/3.2/library/sys.html
 
 from typing import (
-    List, Sequence, Any, Dict, Tuple, TextIO, overload, Optional, Union,
-    TypeVar, Callable, Type,
+    List, NoReturn, Sequence, Any, Dict, Tuple, TextIO, overload, Optional,
+    Union, TypeVar, Callable, Type,
 )
 import sys
 from types import FrameType, TracebackType
-from mypy_extensions import NoReturn
 
 _T = TypeVar('_T')
 

stdlib/3/unittest/__init__.pyi

@@ -1,10 +1,9 @@
 # Stubs for unittest
 
-from mypy_extensions import NoReturn
 from typing import (
     Any, Callable, ContextManager, Dict, FrozenSet, Generic, Iterable, Iterator,
-    List, Optional, overload, Pattern, Sequence, Set, TextIO, Tuple, Type,
-    TypeVar, Union
+    List, NoReturn, Optional, overload, Pattern, Sequence, Set, TextIO, Tuple,
+    Type, TypeVar, Union
 )
 import logging
 import sys