Cleanup extension map

[zach]

• VP6 is a nonexisting format. It's an extensions I used once for one file to distinct between an h263 and a vp6 flv file. It can be removed.
• F4P is the filetype of Adobe's Access DRM servers. It's definitely not supported by HTML5 (nor by our player - only by OSMF).
• 3GP/3G2 (only with H263/H264 video and AAC audio) are supported in Flash. I am not sure if 3GP is supported in HTML5 browsers, but I think in none. IE/Safari probably sticked to MP4 and MP3.
• I don't think the Matroska container is supported by any browser. Perhaps the container works in Chrome, but Chrome doesn't support any of the codecs (MPEG2, XviD, H264) it includes.
• I am not sure about sdp (Icecast/Shoutcast) support in HTML5. Did you test that? We don't want it as a supported format in Flash - rather have a specific, third-party supported provider.

[pablo]

Fixed in [1698]. I left in 3GP since Flash will try to play it. May as well leave it in for HTML5 unless we know for sure it isn't supported.