updater: Move libupdater to Soong.

Test: mmma -j bootable/recovery
Test: Run recovery_unit_test and recovery_component_test on marlin.
Change-Id: I2617b87d13c585addf0ed2fbae8c3ce443ea7200
diff --git a/Android.mk b/Android.mk
index 9888f86..7d13f4c 100644
--- a/Android.mk
+++ b/Android.mk
@@ -14,7 +14,7 @@
 
 LOCAL_PATH := $(call my-dir)
 
-# Needed by build/make/core/Makefile.
+# Needed by build/make/core/Makefile. Must be consistent with the value in Android.bp.
 RECOVERY_API_VERSION := 3
 RECOVERY_FSTAB_VERSION := 2