action_sheet [nfc]: Remove the custom modal sheet we no longer use

Author: sm-sayedi

lib/widgets/draggable_scrollable_modal_bottom_sheet.dart

@@ -623,6 +623,8 @@ void main() {
         .evaluate().length).equals(isShown ? 1 : 0);
       check(find.text(zulipLocalizations.actionSheetOptionQuoteAndReply)
         .evaluate().length).equals(isShown ? 1 : 0);
+      check(find.text(zulipLocalizations.actionSheetOptionMarkAsUnread)
+        .evaluate().length).equals(isShown ? 1 : 0);
       check(find.text(zulipLocalizations.actionSheetOptionCopyMessageText)
         .evaluate().length).equals(isShown ? 1 : 0);
       check(find.text(zulipLocalizations.actionSheetOptionCopyMessageLink)
@@ -634,7 +636,7 @@ void main() {
     }
 
     testWidgets('pressing the button dismisses the action sheet', (tester) async {
-      final message = eg.streamMessage();
+      final message = eg.streamMessage(flags: [MessageFlag.read]);
       await setupToMessageActionSheet(tester, message: message, narrow: TopicNarrow.ofMessage(message));
       checkActionSheet(tester, isShown: true);