configure: remove mp_filter leftover

Pointed out by: ubitux
Signed-off-by: Paul B Mahol <onemda@gmail.com>

configure

@@ -5423,7 +5423,6 @@ enabled ebur128_filter && enabled swresample && prepend avfilter_deps "swresampl
 enabled elbg_filter         && prepend avfilter_deps "avcodec"
 enabled mcdeint_filter      && prepend avfilter_deps "avcodec"
 enabled movie_filter    && prepend avfilter_deps "avformat avcodec"
-enabled mp_filter           && prepend avfilter_deps "avcodec"
 enabled pan_filter          && prepend avfilter_deps "swresample"
 enabled pp_filter           && prepend avfilter_deps "postproc"
 enabled removelogo_filter   && prepend avfilter_deps "avformat avcodec swscale"