Fix irace converter and remove irace_converter_hack

[DE0CH]

We can't use pandas2ri.converter or put numpy2ri.converter after ro.default_converter in places where we want to get a ListVector returned from an r function because for some reason ListVector gets converted to OrdDict, which is somehow recognized as a python object, and it tries to call py2rpy. Not sure why. We should logically put numpy2ri.converter on the right of the plus sign because conversion rules on the right of the plus sign overrides conversion rules on the left, and logically, the more specific converter (i.e. numpy2ri) should override the default converter.