Remove unused enum `BizHawkExternalToolUsage`

src/BizHawk.Client.Common/Api/BizHawkExternalToolUsage.cs

@@ -1,23 +0,0 @@
-namespace BizHawk.Client.Common
-{
-	/// <summary>
-	/// This enum describe how an external tool is handled
-	/// </summary>
-	public enum BizHawkExternalToolUsage : short
-	{
-		/// <summary>
-		/// General usage, works even with null emulator
-		/// </summary>
-		Global = 0,
-
-		/// <summary>
-		/// Specific to an emulator (NES,SNES,etc...)
-		/// </summary>
-		EmulatorSpecific = 1,
-
-		/// <summary>
-		/// Specific to a Game
-		/// </summary>
-		GameSpecific = 2
-	}
-}