[integration tests] Don't override the ipc timeout

Summary: The IPC timeout was overriden when introduced to demonstrate the API for the integration tests, but since then this has been copy pasted everywhere with no apparent thought. Remove it and use the default to avoid test timeouts.

Test Plan:

./contrib/teamcity/build-configurations.py chronik-client-integration-tests
./contrib/teamcity/build-configurations.py ecash-lib-integration-tests # Note this doesn't run on my machine

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16083