build: remove wrong avcodec dep in decimate

This was probably a mistake with mpdecimate. The decimate filter doesn't
depend on avcodec.

configure

@@ -5253,7 +5253,6 @@ enabled amovie_filter       && prepend avfilter_deps "avformat avcodec"
 enabled aresample_filter    && prepend avfilter_deps "swresample"
 enabled asyncts_filter      && prepend avfilter_deps "avresample"
 enabled atempo_filter       && prepend avfilter_deps "avcodec"
-enabled decimate_filter     && prepend avfilter_deps "avcodec"
 enabled deshake_filter      && prepend avfilter_deps "avcodec"
 enabled ebur128_filter && enabled swresample && prepend avfilter_deps "swresample"
 enabled elbg_filter         && prepend avfilter_deps "avcodec"