There's an extension for that!
I found that the gnome shell bottom panel very interfering and annoying, especially since I use auto hide in Avant Window Navigator(AWN). There are times that I struggled just to get to AWN icons because it was blocked by occasionally popping out bottom bar.
Download and install gnome-shell-extension-remove-bottom-bar.
You have to install gnome-tweak-tool (via Ubuntu Software Center or Synaptic) first, to let you install extensions and manages them.
|remove bottom bar extension|
I am a little disappointed though, a customization as simple as this should be included in basic setting, not an extension.
keyword : remove, bottom, bar, panel, message, tray, notification, gnome shell