Remove the spawn by the Spawn Button

I saw some topics talkin' about removing the Spawn Button and someone said that is not possibile so I want just to make them unusable.

This is what happens on my gamemode:

http://ift.tt/1iqhFrX

I want to do that when an user press the spawn button or the arrows nothing happens so the only way to log-in is by using the dialog I create.

I guess is possible because I saw it on a gamemode.