gluon-config-mode: fix unsetting of the contact info

package/gluon-config-mode/files/usr/lib/lua/luci/model/cbi/gluon-config-mode/wizard.lua

@@ -125,7 +125,7 @@ function f.handle(self, state, data)
     if data._contact ~= nil then
       uci:set("gluon-node-info", uci:get_first("gluon-node-info", "owner"), "contact", data._contact)
     else
-      uci:set("gluon-node-info", uci:get_first("gluon-node-info", "owner"), "contact")
+      uci:delete("gluon-node-info", uci:get_first("gluon-node-info", "owner"), "contact")
     end
     uci:save("gluon-node-info")
     uci:commit("gluon-node-info")