boot: zephyr: boards: stm32h573i_dk: remove conf file

STM32_MEMMAP is no longer needed since it is now set on the Zephyr side
in the board's 'Kconfig.defconfig' when building MCUboot app.

Also, BOOT_MAX_IMG_SECTORS_AUTO is no longer needed to be disabled after
including the 'soc-nv-flash' binding in the 'st,stm32-xspi-nor' binding,
then adding the 'erase-block-size' and 'write-block-size' properties
in external Flash DT node.

Signed-off-by: Tim Pambor <[email protected]>

Author: tpambor