clean python 3 specific stuff from stdlib/@python2 stubs (#5451)

stdlib/@python2/pstats.pyi

@@ -7,19 +7,6 @@ from typing import IO, Any, Dict, Iterable, List, Optional, Text, Tuple, TypeVar
 _Selector = Union[str, float, int]
 _T = TypeVar("_T", bound=Stats)
 
-if sys.version_info >= (3, 7):
-    from enum import Enum
-    class SortKey(str, Enum):
-        CALLS: str
-        CUMULATIVE: str
-        FILENAME: str
-        LINE: str
-        NAME: str
-        NFL: str
-        PCALLS: str
-        STDNAME: str
-        TIME: str
-
 class Stats:
     sort_arg_dict_default: Dict[str, Tuple[Any, str]]
     def __init__(