Revert "REQ-3345: 直接解散群"

This reverts commit 74726858e7.

im-center-server/src/main/java/cn/axzo/im/group/GroupManager.java

@@ -68,7 +68,8 @@ public class GroupManager {
         return transactionTemplate.execute(unused -> {
             Group savedGroup = groupDao.findByBizCode(request.getBizCode(), request.getGroupType(), true)
                     .orElse(null);
-            BizAssertions.assertTrue(savedGroup == null, String.format("群已经存在: %s", request.getName()));
+            BizAssertions.assertTrue(savedGroup == null || savedGroup.isDismissed(),
+                    String.format("群已经存在: %s", request.getName()));
             ImAccounts imAccounts = accountService.getAccountsByPersons(request.getPeople());
             String owner = imAccounts.findAccount(request.getOwner()).orElse(null);
             BizAssertions.assertNotNull(owner, "群主没有IM账号, 无法创建群. {}", request.getOwner());