Remove icons in taskbar via VNC: Alt + right click not working: other way?

[r0tati0n]

I'd like to customize the taskbar by adding a few symbols.
Ya know... in stock Kali there are two symbols: Iceweasel and Terminal.

I't like to remove the Terminal symbol this is being done by pressing "Alt" plus Right mouse button.
But not via VNC, then the Remmina menu shows up, but not the Remove button of Gnome3Fallback for removing the icon.

Is there another way to remove the icons via VNC?