revert useless sorter change

Author: liamappelbe

pkgs/ffigen/lib/src/visitor/sorter.dart

@@ -22,15 +22,12 @@ class SorterVisitation extends Visitation {
   // all other types.
   static String originalNameSortKey(Binding binding) =>
       '${_typeKey(binding)} ${binding.originalName}';
-  // '~' comes after all valid Dart naming characters.
-  static const _lowPriorityTypes = {
-    'ObjCCategory': '~ObjCCategory',
-    'ObjCProtocol': '~ObjCProtocol',
-    'ObjCMethod': '~~ObjCMethod',
-  };
+  static const _lowPriorityTypes = {'ObjCCategory', 'ObjCProtocol'};
   static String _typeKey(Object o) {
     final t = '${o.runtimeType}';
-    return _lowPriorityTypes[t] ?? t;
+    // '~' comes after all valid Dart naming characters.
+    if (_lowPriorityTypes.contains(t)) return '~$t';
+    return t;
   }
 
   @override