Note class should not be sortable

There are various different methods of sorting an note.

lib/core/note.dart

@@ -18,7 +18,7 @@ enum NoteLoadState {
   NotExists,
 }
 
-class Note with ChangeNotifier implements Comparable<Note> {
+class Note with ChangeNotifier {
   NotesFolder parent;
   String _filePath;
 
@@ -232,19 +232,4 @@ class Note with ChangeNotifier implements Comparable<Note> {
   String toString() {
     return 'Note{filePath: $_filePath, created: $created, modified: $modified, data: $_data}';
   }
-
-  @override
-  int compareTo(Note other) {
-    if (other == null) {
-      return -1;
-    }
-
-    var dt = modified ?? created ?? fileLastModified;
-    var otherDt = other.modified ?? other.created ?? other.fileLastModified;
-    if (dt == null || otherDt == null) {
-      return _filePath.compareTo(other._filePath);
-    }
-
-    return dt.compareTo(otherDt);
-  }
 }

test/note_storage_test.dart

@@ -56,8 +56,9 @@ void main() {
         loadedNotes.add(note);
       });
 
-      loadedNotes.sort();
-      notes.sort();
+      var sortFn = (Note n1, Note n2) => n1.filePath.compareTo(n2.filePath);
+      loadedNotes.sort(sortFn);
+      notes.sort(sortFn);
 
       expect(loadedNotes, notes);