CIF code generator always generates an enum, even when not needed

We have them fixed in the template. In !710 (merged) we fix the bug that if there is none, we get invalid output.

But, to properly address this, we should not generate an enum at all, if there is none. So, take those fixed parts out of the templates for the various languages, and only have the placeholder. The fixed parts are then generated as part of the text that replaces the placeholder, in case there is an enum. Otherwise the placeholder is replaced by no text.