tests for twisted.protocols.dict raise deprecation errors

[eevelweezel]

Running the tests for twisted.protocols.dict raise deprecation errors. This module was deprecated in 17.9, so the cleanest way to resolve this is to remove it.

To repro, run the test case from #10149

While working on #11712, it was requested that the removal of twisted.protocols.dict move to a separate ticket, so I'm creating one under which to do that work.