Revert "Cleanup unused confirm target in GetMinimumFee()"

Summary:
This reverts commit cb2f3c887ce97dae40cf6cb4c8891b36e74b94bb.
Breaks master since it depends on D2543

Test Plan: N/A

Reviewers: deadalnix, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2601