Remove needless timeout in functional test

Summary: Overriding the timeout might be useful during debugging, but for production it only prevents the config dependent timeouts to apply and will cause spurious failures.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_proof_voting

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13179