Remove redundant connect_nodes call in abc-parkedchain.py

Summary:
setup_network does this automatically, so this call is redundant.
Originally, I discovered this while looking for the root cause of this test's
flakiness.

Test Plan:
for i in {1..150}; do ./test_runner.py abc-parkedchain; done
Test is still flaky, but passes 99%+ of the time with this change still.

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2189