tests|samples/bluetooth: Fix sysbuild due to BOAD_IDENTIFIER

After https://github.com/zephyrproject-rtos/zephyr/pull/70438
got merged simultaneously with
https://github.com/zephyrproject-rtos/zephyr/pull/70564


all these tests stopped building properly due to the
change of avaliable variables in Kconfig & cmake.
Let's fix them.
As a bonus, as for kconfig the BOARD_TARGET_STRING is the
same for the hwmv1 backwards compatible name, let's
just remove the check for the old names.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>