Gnome 3 has changed the defult key combination for moving files to trash to CTRL-Del. To switch it back first install the dconf-editor.
Run the dconf-editor by pressing ALT-F2.
Tick the org -> gnome -> desktop -> interface -> can-change-accels option.
Now, in nautilus, select whatever file or folder, open the Edit menu and hover the mouse over the Move to Trash option. Then, with the trash selected, press the Del key twice. The first press clears the keyboard shortcut, and the second press assigns it as the keyboard shortcut.
You should change can-change-accels option to desable again to not allow accidentally changes