Nuke high efficiency video coding

BUR #43889 is pending approval.

nuke high_efficiency_video_coding

This seems like an unnecessary tag given that the search exif:"FFmpeg:VideoCodec=hevc" that's also linked in the high efficiency video coding wiki accomplishes the same purpose while also always being up to date.

Forgot to add that exif:"FFmpeg:VideoCodec=hevc" is not as convenient in comparison, sure, but I think that should be resolved by adding a metatag similar to filetype:mp4 and the like instead of manually tagging it on posts.

If it's something that can be automatically detected via metadata, it can probably be auto-tagged by the site similarly to tags such as highres, video, sound, etc.