overlays: bcm2711: Remove I/O pinctrl references

Now that the base bcm2711 base dts files give the added I/O interfaces
references to the default pinctrl nodes, remove the same from their
respective overlays.

See: https://github.com/raspberrypi/linux/pull/5443



Signed-off-by: Phil Elwell <phil@raspberrypi.com>