Deprecate mistral from st2ci

[amanda11]

Remove mistral and postgres from st2ci workflows as part of the Mistral deprecation

Addresses st2ci from StackStorm/st2#4762

[amanda11]

A few queries:

1. Is the backup workflow needed - if I take out the mistral it doesn't really seem to do much, and I think was only referenced from the mistral work packages
2. Not sure what testing I can do on this, I'm going to test installation of it as a pack, but other than that - is there much to do?
3. What calls these workflows, as the mistral ones are removed, and I wans't sure if things needed to change to call different setup workflows or backup etc?

[blag]

1. I kept the backup_logs workflow. I don't think this is still used since we switched to using a log aggregation server, but we'll keep it around just in case.
2. No testing. We test this in production. And for promotion workflows, we test those during releases. It's fun.
3. As long as we change or remove all of the workflows/rules that use changed/removed workflows, it should be fine. The st2cd pack calls st2ci workflows and vice versa, but that's the extent of the changes we need to worry about.

Ideally, the the st2ci pack should be self contained, and not call any st2cd workflows. And the st2cd pack should only run st2ci workflows as part of testing before deploying. But I digress...

This looks good. 👍

[punkrokk]

LGTM