lib/search/kanji: make taughtIn into int?

lib/search/kanji_search.dart

@@ -179,19 +179,6 @@ Future<KanjiSearchResult?> searchKanjiWithDbConnection(
       entry['type'] as String: entry['ref'] as String,
   };
 
-  final String? grade = {
-    1: 'grade 1',
-    2: 'grade 2',
-    3: 'grade 3',
-    4: 'grade 4',
-    5: 'grade 5',
-    6: 'grade 6',
-    7: 'grade 7',
-    8: 'grade 8',
-    9: 'grade 9',
-    10: 'grade 10',
-  }[entry['grade'] as int?];
-
   final String? jlptLevel = {
     5: 'N5',
     4: 'N4',
@@ -202,7 +189,7 @@ Future<KanjiSearchResult?> searchKanjiWithDbConnection(
 
   return KanjiSearchResult(
     kanji: entry['literal']! as String,
-    taughtIn: grade,
+    taughtIn: entry['grade'] as int?,
     jlptLevel: jlptLevel,
     newspaperFrequencyRank: entry['frequency'] as int?,
     strokeCount: entry['strokeCount'] as int,