There are a few old oEmbed caches which have the title saved in binary
(because they contain Chinese characters). This fails with
`ActionView::Template::Error ("å" from ASCII-8BIT to UTF-8)`. Since I
found only very old OEmbed caches with this problem (newest from 2012),
I think we can just remove these. When I create a new oEmbed cache for
the same URL it creates it without `!binary`.

closes #7620