[CI] Setup don't need to be a function

Summary:
This was historically called in several places but this has not been the
case for a while. Also move a few declarations to make the flow more
logical.

Test Plan: Run any CI build plan.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D6689