UI Freeze break request for control-center/wifi

Hi,

This is a very minor UI change but it can be misleading so we decided
to drop before the stable release.

https://bugzilla.gnome.org/793238

There's now (git master) a refresh button in the Wifi list which is
supposed to trigger manually the scan for new networks. Considering
https://bugzilla.gnome.org/793238#c0 we want to revert the commit that
introduced this feature.

It pretty much consists of hiding the button in the screenshot below:

https://i.imgur.com/JOl3no2.png

Thanks,
Felipe.