Vote for the below idea if the below workaround didn’t work in your case.
To remove none option on a picklist in Salesforce, follow the below steps
1. Edit
your page layout and make your picklist field a required field by clicking on
the properties and checking “Required” check box.
2. Click “Ok” button.
3. Save the the changes to the page layout. This will remove
the “-None-” as an option in the picklist.
Output:
