On the iPhone you need to be in the playlist view - the stack icon in the top right toggles between the playlist and the details of the track now playing - and select "Action" from the bottom of the screen.
The "Clear Now Playing" option is there.
On the iPad select the play icon at the top right and it should launch the Now Playing View, there will be an Action button either at the top or mid screen depending on your view. Hit that and you'll see Clear "Now Playing"
