Darnit, I already wrote the rest of the comment below before noticing the "iOS" part of your comment. These are all Firefox add-ons for the desktop. Still, I'll post them in case they're useful to anyone else.
I use the unhook add-on for that, it removes all recommended videos:
youtube-audio lets you disable the video-feed. Nice when you're using it to listen to what are basically podcasts and you don't want to waste bandwidth: