Remove unused methods

src/background/repositories/PersistentSettingRepository.js

@@ -1,10 +1,6 @@
 import Setting from '../domains/Setting';
 
 export default class SettingRepository {
-  save(settings) {
-    return browser.storage.local.set({ settings: settings.serialize() });
-  }
-
   async load() {
     let { settings } = await browser.storage.local.get('settings');
     if (!settings) {

src/background/usecases/SettingUseCase.js

@@ -9,10 +9,6 @@ export default class SettingUseCase {
     this.settingRepository = new SettingRepository();
   }
 
-  save(settings) {
-    this.persistentSettingRepository.save(settings);
-  }
-
   get() {
     return this.settingRepository.get();
   }