Don't expose a user's private token in the `/api/v3/user` API.

- This would allow anyone with a personal access token (even a read-only
  token, once scopes are implemented) to escalate their access by
  obtaining the private token.

doc/api/users.md

@@ -310,8 +310,7 @@ GET /user
   "can_create_group": true,
   "can_create_project": true,
   "two_factor_enabled": true,
-  "external": false,
-  "private_token": "dd34asd13as"
+  "external": false
 }
 ```
 

lib/api/users.rb

@@ -327,7 +327,7 @@ module API
       # Example Request:
       #   GET /user
       get do
-        present @current_user, with: Entities::UserLogin
+        present @current_user, with: Entities::UserFull
       end
 
       # Get currently authenticated user's keys

spec/requests/api/users_spec.rb

@@ -605,6 +605,7 @@ describe API::API, api: true  do
       expect(json_response['can_create_project']).to eq(user.can_create_project?)
       expect(json_response['can_create_group']).to eq(user.can_create_group?)
       expect(json_response['projects_limit']).to eq(user.projects_limit)
+      expect(json_response['private_token']).to be_blank
     end
 
     it "returns 401 error if user is unauthenticated" do