Remove `ServiceInjector.ClearServices`

This call in `ToolManager.Restart` was to set `[{Optional.Required}Service]`
props to `null`, but the tool form would get `Close`d immediately afterwards, so
it never gets the chance to hit the `null` path if one exists. However, some
tools are written as though they keep the stale value, for example attempting to
call a cleanup function on it in their `Closed` event handler. These will now
work as intended.
`[OptionalService]`s that can't be satisfied are set to `null` by
`ServiceInjector.UpdateServices`, so clearing those isn't necessary, and
`ClearServices` has no other usages.

src/BizHawk.Client.EmuHawk/tools/ToolManager.cs

@@ -598,7 +598,6 @@ namespace BizHawk.Client.EmuHawk
 				else
 				{
 					unavailable.Add(tool);
-					ServiceInjector.ClearServices(tool); // the services of the old emulator core are no longer valid on the tool
 					if (tool is IExternalToolForm) ApiInjector.ClearApis(tool);
 				}
 			}

src/BizHawk.Emulation.Common/ServiceInjector.cs

@@ -10,22 +10,6 @@ namespace BizHawk.Emulation.Common
 	/// </summary>
 	public static class ServiceInjector
 	{
-		/// <summary>
-		/// clears all services from a target
-		/// </summary>
-		public static void ClearServices(object target)
-		{
-			Type targetType = target.GetType();
-			object?[] tmp = { null };
-
-			foreach (var propInfo in
-				targetType.GetPropertiesWithAttrib(typeof(RequiredServiceAttribute))
-				.Concat(targetType.GetPropertiesWithAttrib(typeof(OptionalServiceAttribute))))
-			{
-				propInfo.GetSetMethod(true).Invoke(target, tmp);
-			}
-		}
-
 		/// <summary>
 		/// Feeds the target its required services.
 		/// </summary>