SYMPTOM:
It is not supported to disable the Mobile license for Strategy Administrator account in Strategy Developer 10.x
REPRODUCE STEPS:
1. Login Developer with "Administrator"
2. Go to Administration > User Manager > Everyone and find user "Administrator"
3. Edit Administrator and go to Project Access. Try to uncheck the Mobile related privilege but failed, as shown below:

CAUSE:
It is working by design that it is not allowed to modify privileges for Administrator because it is unique in Metadata and designed to have all privileges.
WORKAROUND:
Duplicate user Administrator to another account and then modify the privileges for the duplicated one.