boot: zephyr: boards: nrf52840dk: Fix overlay

Fixes an issue with a node which has been removed from zephyr.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

Author: nordicjm

boot/zephyr/boards/nrf52840dk_qspi_nor_secondary.overlay

@@ -7,7 +7,6 @@
 /delete-node/ &boot_partition;
 /delete-node/ &slot0_partition;
 /delete-node/ &slot1_partition;
-/delete-node/ &scratch_partition;
 
 &flash0 {
 	partitions {