Don't set the build id if we need to append the digest

Background in http://go/compatible-build-fingerprint. If we want
to append unique vbmeta digest to build id, we cannot setup the
prop value at build time. Instead, set the old value as
ro.build.legacy.id; and let init set ro.build.id at runtime.

Bug: 186786987
Test: build a target file with the flag on
Change-Id: Ie139725bb7e5c65bd3f28f43b9975ba48ee10354
diff --git a/core/sysprop.mk b/core/sysprop.mk
index daebdd3..0fc96e0 100644
--- a/core/sysprop.mk
+++ b/core/sysprop.mk
@@ -260,6 +260,7 @@
 	        BUILD_HOSTNAME="$(BUILD_HOSTNAME)" \
 	        BUILD_NUMBER="$(BUILD_NUMBER_FROM_FILE)" \
 	        BOARD_BUILD_SYSTEM_ROOT_IMAGE="$(BOARD_BUILD_SYSTEM_ROOT_IMAGE)" \
+	        BOARD_USE_VBMETA_DIGTEST_IN_FINGERPRINT="$(BOARD_USE_VBMETA_DIGTEST_IN_FINGERPRINT)" \
 	        PLATFORM_VERSION="$(PLATFORM_VERSION)" \
 	        PLATFORM_VERSION_LAST_STABLE="$(PLATFORM_VERSION_LAST_STABLE)" \
 	        PLATFORM_SECURITY_PATCH="$(PLATFORM_SECURITY_PATCH)" \