Even simpler - just click on the waveform where you want to split it, and hit 's' on your keyboard. Then select the portion to the left of the vocal and delete it.
Or, 'slip edit' the waveform - hover your cursor over the centre of the far left end of the clip and drag it all the way back to where the vocal starts.
All these functions are readily available in the help files included with the software by the way.