Rename `cause` field in JSONIOTst.

[PaulKlint]

Describe the bug

There are incompatible declarations for the field cause in RuntimeException.

To Reproduce

In Exception we have:

data RuntimeException 
    = ...
    | Java(str class, str message)             // deprecated
    | Java(str class, str message, RuntimeException cause) // deprecated
    |  ...
;

In lang::rascalcore::compile::Examples::JSONIOTst we have

data RuntimeException(str cause="");

When these modules are included in the same scope we get the warning that the two fields cause overlap.

Proposed solutions

• Since the Java constructors seem to be deprecated we can remove them.
• Rename the cause field in JSONIOTst

[DavyLandman]

I vote for changing the example module.