Merge cleanup: remove an unused variable

Author: piki

storage/innobase/handler/ha_innodb.cc

@@ -22049,7 +22049,6 @@ static MYSQL_SYSVAR_STR(extra_system_table_prefixes,
                         "Additional prefixes that designate system (not user) tables for metrics accounting.",
                         nullptr, nullptr, nullptr);
 
-extern uint srv_flush_log_at_timeout;
 static MYSQL_SYSVAR_UINT(flush_log_at_timeout, srv_flush_log_at_timeout,
                          PLUGIN_VAR_OPCMDARG,
                          "Write and flush logs every (n) second.", nullptr,