gluon-setup-mode: remove unneeded require

package/gluon-setup-mode/luasrc/lib/gluon/upgrade/310-setup-mode-migrate

 #!/usr/bin/lua
 
-local site = require 'gluon.site_config'
 local uci = require 'luci.model.uci'
 
 local c = uci.cursor()