Remove Type from FitParameters

[spflueger]

Currently there is a Type attribute attached to FitParameters in the AmplitudeModel. These are remnants of the old c++ code and it should verified if there is any merit in keeping them.

A type could be useful for definition of a complex valued Parameter: Magnitude + Phase or Real + Imaginary (see ComPWA/tensorwaves#161)

[redeboer]

A type could be useful for definition of a complex valued Parameter: Magnitude + Phase or Real + Imaginary (see ComPWA/tensorwaves#161)

This can be handled more easily when #384 is through. One can then start to define different types of FitParameter as attr.s classes with an inheritance hierarchy similar to the dynamics. With attr.asdict it's then easy to dump those FitParameter to a dict and add a "type": <class name>, just like is done for Dynamics classes.