Removed unused import symbols from stdlib stubs and fixed a few other errors detected by pyright. I did a similar pass several months ago; these were introduced since then. (#4803)

Co-authored-by: Eric Traut <erictr@microsoft.com>

stdlib/3/asyncio/futures.pyi

@@ -1,6 +1,6 @@
 import sys
 from concurrent.futures._base import Error, Future as _ConcurrentFuture
-from typing import Any, Awaitable, Callable, Generator, Iterable, List, Optional, Tuple, Type, TypeVar, Union
+from typing import Any, Awaitable, Callable, Generator, Iterable, List, Optional, Tuple, TypeVar, Union
 
 from .events import AbstractEventLoop
 

stdlib/3/asyncio/trsock.pyi

@@ -1,7 +1,7 @@
 import socket
 import sys
 from types import TracebackType
-from typing import Any, BinaryIO, Iterable, List, NoReturn, Optional, Sequence, Tuple, Type, Union, overload
+from typing import Any, BinaryIO, Iterable, List, NoReturn, Optional, Tuple, Type, Union, overload
 
 if sys.version_info >= (3, 8):
     # These are based in socket, maybe move them out into _typeshed.pyi or such