boards/qemu_x86: remove stale flash reference from qemu_x86_long
boards/qemu_x86: remove stale flash reference from qemu_x86_long

The QEMU x86 .dts files were re-arranged before long mode was
merged. We don't need this reference to the flash region anymore.

Signed-off-by: Charles E. Youse <5bc2c6f24e92b68873229a004438f1d6a77a3862@intel.com>

Vudentz/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr