updater_sample: add proguard.flags

Test: on device
Change-Id: Ia8582053b7330d06e618f2555332cfb2a89b3df8
Signed-off-by: Zhomart Mukhamejanov <zhomart@google.com>
diff --git a/updater_sample/Android.mk b/updater_sample/Android.mk
index 7662111..463dbb3 100644
--- a/updater_sample/Android.mk
+++ b/updater_sample/Android.mk
@@ -21,8 +21,7 @@
 LOCAL_MODULE_TAGS := samples
 LOCAL_SDK_VERSION := system_current
 
-# TODO: enable proguard and use proguard.flags file
-LOCAL_PROGUARD_ENABLED := disabled
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
 LOCAL_SRC_FILES := $(call all-java-files-under, src)