[Misc] DiffusionWorker, MultiprocDiffusionExecutor: cleanup unused references to zmq

[NickCao]

Purpose

While reading zmq related code, I noticed that zmq context is initialized in several placed but never used, thus the cleanup.

Test Plan

pytest -s -v tests/e2e/offline_inference/test_zimage_parallelism.py

Test Result

================== 2 passed, 17 warnings in 123.94s (0:02:03) ==================

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[hsliuustc0106]

does it help initialization speed?

[NickCao]

does it help initialization speed?

zmq Context takes no time to init, so no. But removing these unused references can prevent confusion that the workers are still using zmq for IPC while they actually are not.