[nrf fromtree] boot: zephyr: boards: remove nrf54h20dk overlay

The nrf54h20dk overlay is no longer required as the gpio pad groups
have been removed.

Signed-off-by: Bjarki Arge Andreasen <[email protected]>
(cherry picked from commit 71b41e38e9f5d278178be17f6d42f2559f8e46aa)

Author: bjarki-andreasen