OptaShift employee rostering: remove that one arquillian test on 7.5.x that fails in the productized build

In optaplanner 7.5.x, optashift-employee-rostering has 1 trivial arquillian test. On master, we've replaced it with cargo tests and we're increasing test coverage.

That 1 arquillian test on optaplanner 7.5.x works in community, but in the DM 7.0 build, it apparently fails as reported by Mikhail here: BXMSPROD-1. Because we want customers to customize that template, that code should always just build with "mvn clean build" without errors.

Fixing it would mean fixing arquillian's version mess, something we struggle with for days for every arquillian upgrade. The proposal is to be practical about this and simply remove that arquillian test on 7.5.x.