manta: set default USB configuration to "MTP"

Bug: 6679671
Change-Id: Iec3c64f7442c1e2009a4a2110891a025086a99e2
diff --git a/CleanSpec.mk b/CleanSpec.mk
index e471a64..39228b4 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -48,4 +48,5 @@
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/obj/SHARED_LIBRARIES/libsurfaceflinger_intermediates)
-$(call add-clean-step, rm -rf $(PRODUCT_OUT)/obj/SHARED_LIBRARIES/libui_intermediates)
\ No newline at end of file
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/obj/SHARED_LIBRARIES/libui_intermediates)
+$(call add-clean-step, rm -f $(PRODUCT_OUT)/root/default.prop)