test: remove duplicate test about warning in lib/net.js
test-net-server-simultaneous-accepts-produce-warning-once.js
test a same code as test-net-deprecated-setsimultaneousaccepts.js
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So I remove test-net-server-simultaneous-accepts-produce-warning-once.js
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before coverage: https://coverage.nodejs.org/coverage-895c3d937ea74faa/lib/net.js.html#L1761