Two things here:

1. When we changed the stateCd stuff for readNWISdata, it also changed it for whatNWISsites. Since in whatNWISsites we're still hitting the "waterservices" endpoint (not "waterdata"), we don't want that to happen.
2. A user wanted to do:

whatNWISsites(stateCd = "NY", service="gwlevels") 

That's cool...but it wasn't something we were doing. I added a line that took the service argument and converted it to the appropriate "hasDataTypeCd" argument