boards: Revert "boards: acrn_ehl_crb: Add ibecc DTS node"

This reverts commit 445a23a1.

This change was made with the incorrect assumption that using IBECC in
an ACRN VM is a valid use case. Turns out that ACRN will always manage
the IBECC access itself and the Zephyr driver is only useful for running
natively on the hardware.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>