use AsyncGenerator from typing

Author: JelleZijlstra

test-data/unit/check-async-await.test

@@ -308,7 +308,7 @@ def f() -> Generator[int, str, int]:
 
 [case testAsyncGenerator]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def f() -> int:
     return 42
@@ -330,7 +330,7 @@ async def h() -> None:
 
 [case testAsyncGeneratorManualIter]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def genfunc() -> AsyncGenerator[int, None]:
     yield 1
@@ -347,7 +347,7 @@ async def user() -> None:
 
 [case testAsyncGeneratorAsend]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def f() -> None:
     pass
@@ -367,7 +367,7 @@ async def h() -> None:
 
 [case testAsyncGeneratorAthrow]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def gen() -> AsyncGenerator[str, int]:
     try:
@@ -385,7 +385,7 @@ async def h() -> None:
 
 [case testAsyncGeneratorNoSyncIteration]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def gen() -> AsyncGenerator[int, None]:
     for i in (1, 2, 3):
@@ -403,7 +403,7 @@ main:9: error: AsyncGenerator[int, None] has no attribute "__iter__"; maybe "__a
 
 [case testAsyncGeneratorNoYieldFrom]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def f() -> AsyncGenerator[int, None]:
     pass
@@ -415,7 +415,7 @@ async def gen() -> AsyncGenerator[int, None]:
 
 [case testAsyncGeneratorNoReturnWithValue]
 # flags: --fast-parser --python-version 3.6
-from mypy_extensions import AsyncGenerator
+from typing import AsyncGenerator
 
 async def gen() -> AsyncGenerator[int, None]:
     yield 1