TT grounding issue

It's probably already grounded somehow, (most likely through the interconnects). By adding the ground from the table you are creating a ground loop. Leave it off, no problem. You might put a piece of tape on the end of the wire so that it doesn't touch anything and short out a component.

Mofimadness is correct. No problem
I operate my turntable the same way

Just to add... there is no danger of shorting anything out with the loose ground wire. The worst that could happen, if the bare end touches something, is to re-create another ground loop and thus produce a usually harmless but annoying hum.