Removed marked complete task action (#15211)

Resolves #14869 

### Description
Added new action deletion method to remove "Mark Task Complete".

### Acceptance Criteria
- [ ] BvaDispatchTasks cannot be marked complete by anyone through the caseflow task action dropdown

### Testing Plan
1. Sign in as BVADispatch user White.
2. Navigate to your queue.
3. Select a case.
4. Confirm the action is not there.
5. Sign in as BVADispatch admin Black.
6. Navigate to the team assigned queue.
7. Repeat steps 3. and 4.

app/models/tasks/bva_dispatch_task.rb

@@ -12,6 +12,7 @@ def available_actions(user)
     if assigned_to == user || parent.task_is_assigned_to_organization_user_administers?(user)
       actions.unshift(Constants.TASK_ACTIONS.DISPATCH_RETURN_TO_JUDGE.to_h)
       actions.delete(Constants.TASK_ACTIONS.ASSIGN_TO_TEAM.to_h)
+      actions.delete(Constants.TASK_ACTIONS.MARK_COMPLETE.to_h)
     end
 
     actions

spec/models/tasks/bva_dispatch_task_spec.rb

@@ -237,5 +237,10 @@
       expect(bva_d_task.available_actions(bva_d_task.assigned_to))
         .not_to include(Constants.TASK_ACTIONS.ASSIGN_TO_TEAM.to_h)
     end
+
+    it "actions should not include 'Mark Task Complete'" do
+      expect(bva_d_task.available_actions(bva_d_task.assigned_to))
+        .not_to include(Constants.TASK_ACTIONS.MARK_COMPLETE.to_h)
+    end
   end
 end