Remove second empty line in mypy_extensions (python#1237)

Author: sixolet

third_party/2and3/mypy_extensions.pyi

@@ -2,7 +2,6 @@ from typing import Dict, Type, TypeVar, Optional, Union
 
 _T = TypeVar('_T')
 
-
 def TypedDict(typename: str, fields: Dict[str, Type[_T]]) -> Type[dict]: ...
 
 def Arg(type: _T = ..., name: Optional[str] = ...) -> _T: ...