use UnmanagedCallersOnly for delegates

src/ARMeilleure/Translation/DelegateInfo.cs

@@ -4,15 +4,10 @@ namespace ARMeilleure.Translation
 {
     class DelegateInfo
     {
-#pragma warning disable IDE0052 // Remove unread private member
-        private readonly Delegate _dlg; // Ensure that this delegate will not be garbage collected.
-#pragma warning restore IDE0052
-
         public IntPtr FuncPtr { get; }
 
-        public DelegateInfo(Delegate dlg, IntPtr funcPtr)
+        public DelegateInfo(IntPtr funcPtr)
         {
-            _dlg = dlg;
             FuncPtr = funcPtr;
         }
     }