[nrf noup] boot/zephyr: update nrf54l15dk ext flash configs

nrf-squash! [nrf noup] boot/zephyr: add nrf54l15dk ext flash configs

Fprotect is enabled by default, size of MCUboot must be less
than 62KB. Removed PM_PARTITION_SIZE_MCUBOOT to use the default
value.
Fixes NCSDK-35436

Signed-off-by: Grzegorz Chwierut <[email protected]>

Author: gchwier

boot/zephyr/boards/nrf54l15dk_nrf54l15_cpuapp_ext_flash.conf

@@ -1,7 +1,6 @@
 CONFIG_SPI=y
 CONFIG_SPI_NOR=y
 CONFIG_FLASH=y
-CONFIG_PM_PARTITION_SIZE_MCUBOOT=0x14000
 CONFIG_MAIN_STACK_SIZE=20480
 CONFIG_BOOT_MAX_IMG_SECTORS=512
 CONFIG_SPI_NOR_FLASH_LAYOUT_PAGE_SIZE=4096