To disable the Application Directory from WF-Client, we can disable some of the privileges for that specific user from the Admin Console > Security Centre.

Follow the below steps to disable Application Directory :
1. Create a New role (to avoid giving reporting server privileges) with below instructions :
>> In Advanced Reporting , check everything except these 2 with ID as 
 a.) opVisuaisation, b.) opUloadDataFile, 
>> In Application Development check everything except these 2 with ID as  
a.) opMetadata, b.) opServerConsole, 
>> In Group Administration, check everything.
>> In Administration check everything except the one with ID as a.) opRevSrvProps

2. Create a New Group > Right click Group > Security > Rules > From group Tab > Select your Group > at bottom Select your Role and Permit it. > Click ok.
3. Create a New user > assign the user to the group.
4. Go to Workspaces > Right click on workspaces > Security > Rules > From group Tab > Select your Group > at bottom Select your Role and Permit it. > Click ok.
5. Login as that new user and check.