Cleanup: Remove unused runtime field from the MovieClip

It is a part of old-standing TODO, and code which accesses
the value was commented out for many years.

Remove the field to help with an upcoming const-correctness
improvements.

source/blender/blenkernel/intern/movieclip.c

@@ -1344,7 +1344,6 @@ static ImBuf *movieclip_get_postprocessed_ibuf(
   }
 
   if (ibuf) {
-    clip->lastframe = framenr;
     real_ibuf_size(clip, user, ibuf, &clip->lastsize[0], &clip->lastsize[1]);
 
     /* Post-process frame and put to cache if needed. */
@@ -1566,17 +1565,7 @@ bool BKE_movieclip_has_frame(MovieClip *clip, MovieClipUser *user)
 
 void BKE_movieclip_get_size(MovieClip *clip, MovieClipUser *user, int *width, int *height)
 {
-#if 0
-  /* originally was needed to support image sequences with different image dimensions,
-   * which might be useful for such things as reconstruction of unordered image sequence,
-   * or painting/rotoscoping of non-equal-sized images, but this ended up in unneeded
-   * cache lookups and even unwanted non-proxied files loading when doing mask parenting,
-   * so let's disable this for now and assume image sequence consists of images with
-   * equal sizes (sergey)
-   * TODO(sergey): Support reading sequences of different resolution.
-   */
-  if (user->framenr == clip->lastframe) {
-#endif
+  /* TODO(sergey): Support reading sequences of different resolution. */
   if (clip->lastsize[0] != 0 && clip->lastsize[1] != 0) {
     *width = clip->lastsize[0];
     *height = clip->lastsize[1];

source/blender/makesdna/DNA_movieclip_types.h

@@ -65,8 +65,7 @@ typedef struct MovieClip {
 
   /** Sequence or movie. */
   int source;
-  /** Last accessed frame number. */
-  int lastframe;
+  int _pad;
   /** Size of last accessed frame. */
   int lastsize[2];