default realm = "REALM" is always written although not required by CV

[larsbuntemeyer]

I think this is a similar issue as #727. For CORDEX, we have eliminated the realm attribute from the required global attributes (and also from table headers). However, cmor will write a default of realm = REALM (example) no matter what.

[durack1]

@larsbuntemeyer agreed, this could be an opportunity to further reduce hard-coding of global attributes, with such items managed through a required_global_attributes.json input file. If there are other obvious cases like this, ping back on this thread and we'll consider this as the 3.9 cleanup work continues.

It it wasn't obvious, we have realm explicitly defined by mip-cmor-tables (with interpretation, e.g. APmon = atmospheric physics monthly, OPmon = ocean physics monthly, AEday = atmospheric aerosol daily, OBmon = ocean biogeochemistry monthly, etc), so there may be opportunities to further reduce global attribute clutter.

[larsbuntemeyer]

Thanks @durack1 , i'll check in here again if we find something similar!