gluon-core: remove obsolete sysconfig.gluon_version handling

The file /lib/gluon/version/core hasn't existed since early 2014, so
this whole script is obsolete.

package/gluon-core/luasrc/lib/gluon/upgrade/001-upgrade

-#!/usr/bin/lua
-
-local sysconfig = require 'gluon.sysconfig'
-local unistd = require 'posix.unistd'
-
-
-if unistd.access('/lib/gluon/version/core') and not sysconfig.gluon_version then
-  -- This isn't an initial upgrade, so set gluon_version
-  sysconfig.gluon_version = ''
-end