gluon-site: remove PO template, it is maintained in the site-example

Having two POT files will only cause confusion.

package/gluon-site/i18n/gluon-site.pot

-msgid ""
-msgstr "Content-Type: text/plain; charset=UTF-8"
-
-msgid "gluon-config-mode:welcome"
-msgstr ""
-
-msgid "gluon-config-mode:pubkey"
-msgstr ""
-
-msgid "gluon-config-mode:reboot"
-msgstr ""