Option to disable chromecast support

[Lojcs]

I find having a chromecast button on youtube videos stressing as I don't want to risk being two clicks away from casting a video to a tv on the same wifi network.

The #load-media-router-component-extension flag used to control chromecast support, but it seems to be missing in new versions (not sure since when). Which means currently there's no convenient way to disable chromecast support.

Adding an option to disable it in settings (perhaps even on a site-by-site basis), or at least bringing back the flag would be great