Disable the meaningless parts of the UI for A/B.

Bug: http://b/28748484
Change-Id: Ie86a265f4699503471e7c717d65677a916dbd25b
diff --git a/Android.mk b/Android.mk
index 65d123a..9a064f2 100644
--- a/Android.mk
+++ b/Android.mk
@@ -93,6 +93,10 @@
     LOCAL_STATIC_LIBRARIES += libext4_utils_static libz
 endif
 
+ifeq ($(AB_OTA_UPDATER),true)
+    LOCAL_CFLAGS += -DAB_OTA_UPDATER=1
+endif
+
 LOCAL_MODULE_PATH := $(TARGET_RECOVERY_ROOT_OUT)/sbin
 
 ifeq ($(TARGET_RECOVERY_UI_LIB),)