Query to SystemProperties for BLAST Flag

For some reason DeviceConfig is not successfully querying the
value on crosshatch - move to query SystemProperties directly

Bug: 147096935
Test: build, boot, adb shell device_config put
window_manager_native_boot wm_use_blast_adapter true/false + reboot

Change-Id: Ic09d1b4446f948248e4e58a6a4f3dc336131a5d0