The https://github.com/wildfly/wildfly-cekit-modules contains scripts to define and create the datasources for EAP.
The clearing of variables is done here
https://github.com/wildfly/wildfly-cekit-modules/blob/0.18.1/jboss/container/wildfly/launch/datasources/added/launch/datasource-common.sh#L30

And here is the issue that the variable used for the host definition is as
host=$(find_env "${service}_SERVICE_HOST")
while unsetting of the env variable is as
unset ${service}_HOST