Revert "Add color to PhoneAccount objects (2/3)"

This reverts commit 09c1fec085e1e2b350b36cc4fcbcc31865945a51.
diff --git a/Android.mk b/Android.mk
index 395aacc..b272445 100644
--- a/Android.mk
+++ b/Android.mk
@@ -14,7 +14,7 @@
 LOCAL_CERTIFICATE := platform
 LOCAL_PRIVILEGED_MODULE := true
 
-LOCAL_PROGUARD_FLAGS := $(proguard.flags)
+LOCAL_PROGUARD_ENABLED := optimization
 
 # Workaround for "local variable type mismatch" error.
 LOCAL_DX_FLAGS += --no-locals