Prevent email sending on admin dev seed.

The only advantage of having emails is for first time developers to find the password more easily... but I think it is not worth it because:

- it forces every dev (large majority of which not a first time dev) to close those email tabs on every `gitlab:setup`
- it is already well documented on the dev install

So let's nuke them.
Prefer single-quoted strings when you don't need string interpolation or special symbols.