Use Bitcoin ABC instead of Core inc onfigre.ac

Summary: As per title. We'll get our branding, eventually :)

Test Plan:

make check

Verify that

Testsuite summary for Bitcoin ABC 0.14.2

is mentionned.

Reviewers: freetrader, sickpig, awemany, kyuupichan, #bitcoin_abc

Reviewed By: sickpig, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D300