Make sure group1, group2 are really empty in test

spec/lib/gitlab/ldap/group_sync_spec.rb

@@ -280,11 +280,15 @@ describe Gitlab::LDAP::GroupSync, lib: true do
               .with('ldap_group2', kind_of(Gitlab::LDAP::Adapter))
               .and_return(Gitlab::LDAP::Group.new(ldap_group2))
 
+          group1.members.destroy_all
+          group1.ldap_group_links.destroy_all
           group1.ldap_group_links.create(
             cn: 'ldap_group1',
             group_access: Gitlab::Access::DEVELOPER,
             provider: 'ldapmain'
           )
+          group2.members.destroy_all
+          group2.ldap_group_links.destroy_all
           group2.ldap_group_links.create(
             cn: 'ldap_group2',
             group_access: Gitlab::Access::OWNER,