libutils: remove subdirs

no longer used in Android

Test/Bug: none

Change-Id: I155d5ade02527bf47893a8bf8bcbb07b0aae53d8
diff --git a/libutils/Android.bp b/libutils/Android.bp
index 209bf9a..80dcdcb 100644
--- a/libutils/Android.bp
+++ b/libutils/Android.bp
@@ -201,5 +201,3 @@
         "-Werror",
     ],
 }
-
-subdirs = ["tests"]