Remove express dependency

[danjoa]

1. The rule is: you need to add dependencies to the packages you import / require in your code.
2. We don't have such direct usage in our code base in cds-test.
3. If (1) holds true, and (2) as well ⇒ we should not need that dependency, correct?
4. @sap/cds needs express, and it brings it with its dependencies, doesn't it?

[chgeo]

True. I guess express was here for the our own tests only, assuming npm doesn't install it with sap/cds. But that changed somewhen, so that express is there.