[chronik] Electrum: remove extra timeout in chronik_electrum_blockchain

Summary: This timeout was added to make debugging faster and was inadvertently landed. This can cause the slow CI machine to fail.

Test Plan:

./test/functional/test_runner.py chronik_electrum_blockchain

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18130