Ref T1191. The bytes types are BINARY(...), which is fixed-length and zero-pads. These hashes are not 64 characters long, so migrating them to binary ends up with a bunch of zero-padding.

Instead, migrate them to text so we drop the zero padding. It would be vaguely nice to either introduce a varbytes type (ick) or change the hash size to a standard size (nicer) eventually, but this isn't very important.

Will adjust secure.phabricator.com.