arm: boot: dts: beaglex15: Remove ID GPIO

According to latest schematics [1], this board
leaves ID pin floating. It's not connected to
anything at all.

So let's remove it.

[1] https://github.com/beagleboard/beagleboard-x15/blob/master/BeagleBoard-X15_RevA2.pdf



Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Tony Lindgren <tony@atomide.com>