Opportunity for code cleanup in FrankDocModel.createAttributes()

Two tasks of this method can be removed:

1. Currently, a getter that accompanies an attribute setter is used for type checking. The return type of the getter is compared with the argument type of the setter. This check becomes irrelevant because getters may be hidden. Getters that are done with Lombok @Getter will not be visible when the de-lombok step is out of the F!F build.
2. Attributes of an enum type will always have the enum as argument type. The check for getXxxEnum() to find the enum type will become irrelevant and can be removed.

See https://github.com/frankframework/frankframework/issues/6344.