Revert inadvertedly removed dependencies of InputSystem.cs

It was failing to reference PlayerConnection

Author: jfreire-unity

Packages/com.unity.inputsystem/InputSystem/Runtime/InputSystem.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
 using UnityEngine.InputSystem.Haptics;
 using Unity.Collections.LowLevel.Unsafe;
 using UnityEngine.InputSystem.Controls;
@@ -10,8 +11,12 @@
 using UnityEngine.InputSystem.EnhancedTouch;
 using UnityEngine.InputSystem.HID;
 using UnityEngine.InputSystem.UI;
+using UnityEngine.InputSystem.Users;
 using UnityEngine.InputSystem.XInput;
 using UnityEngine.InputSystem.Utilities;
+using Unity.Profiling;
+using UnityEngine.Networking.PlayerConnection;
+
 using System.Linq;
 
 #if UNITY_EDITOR