Clear unneeded TODOs.

Author: Guido van Rossum

mypy/nodes.py

@@ -1706,9 +1706,6 @@ def accept(self, visitor: NodeVisitor[T]) -> T:
 
 class AwaitExpr(Node):
     """Await expression (await ...)."""
-    # TODO: [de]serialize()
-    # TODO: arg type must be AsyncIterator[E] or Generator[E, ..., ...] (or Iterator[E]?)
-    #       and then the return type is E
 
     expr = None  # type: Node