Duplicate using directives can be removed CS-R1122
Anti-pattern
Major
Autofix The using directive allows you to use types defined in a namespace without having to specify the fully qualified namespace. There is absolutely no need to specify a using directive twice. Therefore, it is recommended that you remove such duplicate directives.
Bad Practice
using System;
using System.Text;
using System.Collections.Generic;
using System.Text; // duplicate
Recommended
using System;
using System.Text;
using System.Collections.Generic;