axolotl: Simplify AVB flag logic

* AVB's `--flags 3` argument builds a disabled VBMeta with
  disabled hashtree, so no need to set both flags individually.

Change-Id: Idcd3e38c1524bafaf923438b62d1f34ca100af37
diff --git a/BoardConfig.mk b/BoardConfig.mk
index a6ef85d..5f33853 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -130,8 +130,7 @@
 BOARD_AVB_ENABLE := true
 
 # Build the image with verity pre-disabled - https://android.googlesource.com/platform/external/avb/+/58305521295e51cb52a74d8d8bbaed738cf0767a
-BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --set_hashtree_disabled_flag
-BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flags 2
+BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flags 3
 
 #####