[keyserver] Move mediaFromRow and rawMessageInfoFromRows back to not return a Promise

Summary:
This diff does three things:

1. Reverts D4519
2. Reverts D4520
3. Reverts changes to message-fetchers.js in D4521

I separated this out into its own diff because it has some interlocking parts and I wanted to make sure I did it right / it was reviewed right.

Depends on D4833

Test Plan:

1. Flow
2. I ran keyserver locally and made sure things generally still worked

Reviewers: tomek, atul

Reviewed By: tomek

Subscribers: adrian, abosh

Differential Revision: https://phab.comm.dev/D4834