Warn when events are defined with only abstract parameters

[arian]

For example

statemachine X {
  init start;
  event foo(int32);
  state start {}
}

Here the event foo accepts some arguments, but it cannot be used inside the statemachine, as it doesn't have name.

The parameter is parsed/desugard to a FunDefinitionParameter/1 node. If that happens to be inside an Event/3, it should produce a warning for the programmer.