configure: Do not let the webm muxer suggest external libraries.

This can fail as seen on fate and the usefulness of the suggestion is limited.

configure

@@ -2626,7 +2626,6 @@ w64_muxer_select="wav_muxer"
 wav_demuxer_select="riffdec"
 wav_muxer_select="riffenc"
 webm_muxer_select="riffenc"
-webm_muxer_suggest="libopus_encoder libvorbis_encoder libvpx_vp8_encoder libvpx_vp9_encoder"
 wtv_demuxer_select="riffdec"
 wtv_muxer_select="riffenc"
 xmv_demuxer_select="riffdec"