Clean up unused imports

PluralKit.API/Controllers/MemberController.cs

@@ -1,4 +1,3 @@
-using System.Data;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc;
 using PluralKit.Core;

PluralKit.API/Controllers/SystemController.cs

@@ -1,6 +1,4 @@
-using System;
 using System.Collections.Generic;
-using System.Data;
 using System.Linq;
 using System.Threading.Tasks;
 using Dapper;