Remove Python 3.6 branches from typeshed (#8269)

stdlib/asyncio/subprocess.pyi

@@ -6,10 +6,7 @@ from collections.abc import Callable
 from typing import IO, Any
 from typing_extensions import Literal, TypeAlias
 
-if sys.version_info >= (3, 7):
-    __all__ = ("create_subprocess_exec", "create_subprocess_shell")
-else:
-    __all__ = ["create_subprocess_exec", "create_subprocess_shell"]
+__all__ = ("create_subprocess_exec", "create_subprocess_shell")
 
 if sys.version_info >= (3, 8):
     _ExecArg: TypeAlias = StrOrBytesPath