[mining] Ensure sigops and fees follow transactions during sorting

Summary:
Ensure that sigOpCount and fees are attached to the proper transaction
when sorting for CTOR.

Test Plan:

make check && ./test/functional/test_runner.py --extended

Reviewers: #bitcoin_abc, jasonbcox, akb, deadalnix

Reviewed By: #bitcoin_abc, jasonbcox, akb, deadalnix

Subscribers: akb, teamcity, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D2047