Remove constructor bodies in ibor and overnight indexes

[eltoder]

This looks like a confusion with %extend syntax for constructors[1]. These are regular constructors, so the syntax is wrong, but the bodies are ignored by SWIG anyway.

[1] https://www.swig.org/Doc4.1/Python.html#Python_nn43

[eltoder]

@pcaspers Could you take a look please?

[eltoder]

@rolandlichters maybe you can take a look? thanks!

[eltoder]

@pcaspers friendly ping

[pcaspers]

@eltoder same as for the other PR, will merge this soon.

[eltoder]

@pcaspers Any updates on this please?

[pcaspers]

@eltoder apologies, this fell between the cracks. I just ran the change through our tests and merge it here now too. Thanks for spotting this and providing the fix.

[eltoder]

Thank you!