Don't make MotionVectors a subclass of Sequence

It breaked limited api.

Author: WyattBlue

av/sidedata/motionvectors.py

@@ -1,5 +1,3 @@
-from collections.abc import Sequence
-
 import cython
 from cython.cimports import libav as lib
 from cython.cimports.av.sidedata.sidedata import SideData
@@ -8,7 +6,7 @@
 
 
 @cython.cclass
-class MotionVectors(SideData, Sequence):
+class MotionVectors(SideData):
     def __init__(self, sentinel, frame: Frame, index: cython.int):
         SideData.__init__(self, sentinel, frame, index)
         self._vectors = {}

av/sidedata/motionvectors.pyi

@@ -4,7 +4,7 @@ import numpy as np
 
 from .sidedata import SideData
 
-class MotionVectors(SideData, Sequence[MotionVector]):
+class MotionVectors(SideData):
     @overload
     def __getitem__(self, index: int) -> MotionVector: ...
     @overload