Nullification Genes are not compatible with one another

[jan.antilles]

This doesn't seem necessary. Anaerobic and Thermal Resist are already made through gene combinations/splicing. This change would be confusing and unintuitive, and I don't see a purpose for it other than "make Genetics focus more on things that aren't helpful to the crew."

Space is plenty dangerous. Let's not make a department less useful to the entire station.