Removed unused usings. (#3593)

* Removed unused usings.

* Added back using, now that it's used.

* Removed extra whitespace.

Ryujinx.HLE/HOS/Applets/SoftwareKeyboard/KeyboardInputMode.cs

@@ -1,10 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace Ryujinx.HLE.HOS.Applets.SoftwareKeyboard
+namespace Ryujinx.HLE.HOS.Applets.SoftwareKeyboard
 {
     /// <summary>
     /// Active input options set by the keyboard applet. These options allow keyboard