fix: merge DC property

I used dc property as basic property. It was unhealthy.

Author: sudame

lib/domain/rss1_item.dart

@@ -8,19 +8,13 @@ class Rss1Item {
   final String title;
   final String description;
   final String link;
-  final List<String> subjects;
-  final String creator;
-  final DateTime date;
   final DublinCore dc;
   final RssContent content;
 
   Rss1Item({
     this.title,
     this.description,
     this.link,
-    this.subjects,
-    this.creator,
-    this.date,
     this.dc,
     this.content,
   });
@@ -37,12 +31,6 @@ class Rss1Item {
       title: findElementOrNull(element, "title")?.text,
       description: findElementOrNull(element, "description")?.text,
       link: findElementOrNull(element, "link")?.text,
-      subjects: element
-          .findAllElements('dc:subject')
-          .map((subject) => subject.text)
-          .toList(),
-      creator: findElementOrNull(element, 'dc:creator')?.text,
-      date: _dateTimeBuilder(findElementOrNull(element, 'dc:date')?.text),
       dc: DublinCore.parse(element),
       content: RssContent.parse(findElementOrNull(element, "content:encoded")),
     );

test/rss1_test.dart

@@ -108,11 +108,7 @@ void main() {
     expect(firstItem.description, '');
     expect(firstItem.title, 'はてなスタッフのブックマーク拝見！ - 営業マン編「仕事の様々なシーンでフル活用」');
     expect(firstItem.link, 'http://b.hatena.ne.jp/guide/staff_bookmark_03');
-    expect(firstItem.creator, 'sample');
-    expect(firstItem.date, DateTime.parse('2009-04-10T09:44:20Z'));
-    expect(firstItem.subjects[0], 'はてな');
-    expect(firstItem.subjects[1], 'インタビュー');
-    expect(firstItem.subjects[2], 'はてなブックマーク');
+    expect(firstItem.dc.creator, 'sample');
     expect(firstItem.dc.date, '2009-04-10T09:44:20Z');
   });
 }