Remove util.timeout

util.timeout is obsolete since the resolution of BEAM-9009. Its remaining in the codebase is even misleading because it does not override the default pytest timeout (600s), so util.timeout only has an effect when it is set shorter than 600s. It only has a few usages and these can be removed.

https://github.com/apache/beam/blob/6c68bc6c4f44b49c02f966f655e654235d04b365/sdks/python/apache_beam/testing/util.py#L343