Cleanup: Remove dead code

Thanks to Nikita Malyavin for noticing this.
The dead code that was originally introduced in
mysql/mysql-server@b8bd31740cd7088f3a3c164981c7ccda487d301d
was added in commit 2e814d47
to this code base.

storage/innobase/handler/handler0alter.cc

@@ -5424,12 +5424,6 @@ ha_innobase::prepare_inplace_alter_table(
 	if (!(ha_alter_info->handler_flags & ~INNOBASE_INPLACE_IGNORE)) {
 		/* Nothing to do */
 		DBUG_ASSERT(m_prebuilt->trx->dict_operation_lock_mode == 0);
-		if (ha_alter_info->handler_flags & ~INNOBASE_INPLACE_IGNORE) {
-
-			online_retry_drop_indexes(
-				m_prebuilt->table, m_user_thd);
-
-		}
 		DBUG_RETURN(false);
 	}