sysbuild: fix multi image flash

A `west flash` with STLink must not implicitly perform a mass erase on its own.

If a flash erase is required, the option has to be passed manually.

zephyrproject-rtos#69582

boards/st/stm32h573i_dk/board.cmake

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 
-board_runner_args(stm32cubeprogrammer "--erase" "--port=swd" "--reset-mode=hw")
+board_runner_args(stm32cubeprogrammer "--port=swd" "--reset-mode=hw")
 board_runner_args(pyocd "--target=stm32h573iikx")
 
 include(${ZEPHYR_BASE}/boards/common/stm32cubeprogrammer.board.cmake)