Revert "Collection is Sized (python#8977)"

This reverts commit 5bbba5d.

Author: jab

stdlib/builtins.pyi

@@ -804,7 +804,7 @@ class bytearray(MutableSequence[int], ByteString):
     def __alloc__(self) -> int: ...
 
 @final
-class memoryview(Sequence[int]):
+class memoryview(Sized, Sequence[int]):
     @property
     def format(self) -> str: ...
     @property

stdlib/typing.pyi

@@ -452,7 +452,10 @@ class Container(Protocol[_T_co]):
     def __contains__(self, __x: object) -> bool: ...
 
 @runtime_checkable
-class Collection(Sized, Iterable[_T_co], Container[_T_co], Protocol[_T_co]): ...
+class Collection(Iterable[_T_co], Container[_T_co], Protocol[_T_co]):
+    # Implement Sized (but don't have it as a base class).
+    @abstractmethod
+    def __len__(self) -> int: ...
 
 class Sequence(Collection[_T_co], Reversible[_T_co], Generic[_T_co]):
     @overload