Revert "mpeg4videodec: raise an error if sprite_trajectory.table is NULL"

This reverts commit 6ac0e78183.

The mpeg4video parser can reach code that presumes that a certain VLC
has been initialized; yet Libav did not ensure this and Libav bug #1012
[1] is about an ensuing crash.

Instead of fixing the root cause a simple check for whether said VLC
has already been initialized was added; said check is inherently racy.

The proper fix is of course to ensure that the VLC is initialized and
commit 7c76eaeca2 already ensured this,
so there was no need to merge 6ac0e78183
at all. This commit therefore reverts said commit.

[1]: https://bugzilla.libav.org/show_bug.cgi?id=1012

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/mpeg4videodec.c

@@ -197,10 +197,6 @@ static int mpeg4_decode_sprite_trajectory(Mpeg4DecContext *ctx, GetBitContext *g
     if (w <= 0 || h <= 0)
         return AVERROR_INVALIDDATA;
 
-    /* the decoder was not properly initialized and we cannot continue */
-    if (sprite_trajectory.table == NULL)
-        return AVERROR_INVALIDDATA;
-
     for (i = 0; i < ctx->num_sprite_warping_points; i++) {
         int length;
         int x = 0, y = 0;