Overloaded methods should be able to have different return types

[vietj]

The generator inherits from Vert.x 3 the constraint that overloaded methods must have the same return type (e.g void foo() and String foo(int) is forbidden).

This constraint was created to support languages that do not allow method overloading and thus a single method was used to model all overloads.

Since Vert.x 4 we only support generation to languages for which this is not a constraint anymore and thus we can remove this constraint.