Remove useless code causing crash in Targa decoder

Originally committed as revision 19892 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/targa.c

@@ -189,7 +189,6 @@ static int decode_frame(AVCodecContext *avctx,
                 *pal++ = (b << 16) | (g << 8) | r;
             }
             p->palette_has_changed = 1;
-            avctx->palctrl->palette_changed = 0;
         }
     }
     if((compr & (~TGA_RLE)) == TGA_NODATA)