[chronik] Don't sync after each generate in chronik_avalanche

Summary:
The default sync_all is causing a sync of the validation queue to happen which I suspect causes the timeout after a chronik reindex in the test.
Since there is a single node in this test anyway, just avoid syncing everywhere.

Test Plan:

./test/functional/test_runner.py chronik_avalanche

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15081