[avalanche] Remove useless timeout in the tx finalization test

Summary: This timeout was added to speed up debugging during development and was missed during the review.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_transaction_finalization

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17771