Really switch to toybox setprop.

(I forgot to add the symbolic link.)

Change-Id: Iee0dc95ff5c3d848d37861d223b33213588b10f7
diff --git a/Android.mk b/Android.mk
index 195970b..7a3baca 100644
--- a/Android.mk
+++ b/Android.mk
@@ -302,6 +302,7 @@
     sed \
     seq \
     setenforce \
+    setprop \
     setsid \
     sha1sum \
     sleep \