gluon-l3roamd: remove obsolete migration code

package/gluon-l3roamd/luasrc/lib/gluon/upgrade/380-gluon-l3roamd-route

-#!/usr/bin/lua
-local uci = require('simple-uci').cursor()
-
-uci:delete('network', 'l3roam')
-uci:delete('network', 'l3roamd_client')
-
-uci:save('network')