gluon-mesh-batman-adv-core: remove 'gluon.batman_adv' Lua module

It is not used anymore.

package/gluon-mesh-batman-adv-core/files/usr/lib/lua/gluon/batman_adv.lua

-local nixio = require 'nixio'
-
-module 'gluon.batman_adv'
-
-function interfaces(bat_if)
-    local iter = nixio.fs.glob('/sys/class/net/' .. bat_if .. '/lower_*')
-    return function()
-            local path = iter()
-            if path == nil then
-                return nil
-            end
-            local ifname = path:match('/lower_([^/]+)$')
-            return ifname
-        end
-end