Remove typing.AwaitableGenerator

Part of #7580

Author: srittau

stdlib/typing.pyi

@@ -577,7 +577,7 @@ class Awaitable(Protocol[_T_co]):
     @abstractmethod
     def __await__(self) -> Generator[Any, Any, _T_co]: ...
 
-# Non-default variations to accommodate coroutines, and `AwaitableGenerator` having a 4th type parameter.
+# Non-default variations to accommodate coroutines having a 4th type parameter.
 _SendT_nd_contra = TypeVar("_SendT_nd_contra", contravariant=True)
 _ReturnT_nd_co = TypeVar("_ReturnT_nd_co", covariant=True)
 
@@ -598,17 +598,6 @@ class Coroutine(Awaitable[_ReturnT_nd_co], Generic[_YieldT_co, _SendT_nd_contra,
     @abstractmethod
     def close(self) -> None: ...
 
-# NOTE: This type does not exist in typing.py or PEP 484 but mypy needs it to exist.
-# The parameters correspond to Generator, but the 4th is the original type.
-# Obsolete, use _typeshed._type_checker_internals.AwaitableGenerator instead.
-@type_check_only
-class AwaitableGenerator(
-    Awaitable[_ReturnT_nd_co],
-    Generator[_YieldT_co, _SendT_nd_contra, _ReturnT_nd_co],
-    Generic[_YieldT_co, _SendT_nd_contra, _ReturnT_nd_co, _S],
-    metaclass=ABCMeta,
-): ...
-
 @runtime_checkable
 class AsyncIterable(Protocol[_T_co]):
     @abstractmethod