The file you have to edit is /usr/share/unity-2d/shell/launcher/Launcher.qml. Find the items.appendModel(bfbModel); line and remove or comment it.
This is how your /usr/share/unity-2d/shell/launcher/Launcher.qml file with look like after you comment the line i have mentioned:
Next, restart the unity-2d-shell:
$ sudo killall unity-2d-shell