Use unmodified TARGET_USES_VULKAN in ro.hwui.use_vulkan

This will create an empty ro.hwui.use_vulkan if TARGET_USES_VULKAN is
empty.

This matches the make behavior, and helps with validating the contents
of soong vendor filesystem.

Bug: 382295862
Test: lunch aosp_cf_x86_64_phone-trunk_staging-userdebug
Test: m out/soong/.intermediates/build/soong/fsgen/aosp_cf_x86_64_phone_generated_vendor_image/android_common/aosp_cf_x86_64_phone_generated_vendor_image.img
Test: Verified that ro.hwui.use_vulkan is same between make and soong
(empty string)

Change-Id: I9f80e613f7539dd2e895cfa96bd2ba481ddd6974
diff --git a/scripts/gen_build_prop.py b/scripts/gen_build_prop.py
index 5f52d6f..47bbf59 100644
--- a/scripts/gen_build_prop.py
+++ b/scripts/gen_build_prop.py
@@ -450,7 +450,7 @@
   props.append(f"ro.vendor.build.security_patch={config['VendorSecurityPatch']}")
   props.append(f"ro.product.board={config['BootloaderBoardName']}")
   props.append(f"ro.board.platform={config['BoardPlatform']}")
-  props.append(f"ro.hwui.use_vulkan={'true' if config['UsesVulkan'] else 'false'}")
+  props.append(f"ro.hwui.use_vulkan={config['UsesVulkan']}")
 
   if config["ScreenDensity"]:
     props.append(f"ro.sf.lcd_density={config['ScreenDensity']}")