Convert DivinerLiveSymbol to text, not bytes

Summary:
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.

Test Plan: Will adjust `secure.phabricator.com`.

Reviewers: btrahan

Subscribers: epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10613