Clean out *.prop files due to dex2oat instruction-set flag change.

# Move to libc++ as the default STL.

$(call add-clean-step, rm -rf $(OUT_DIR))

# dex2oat instruction-set changes

$(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/build.prop)

$(call add-clean-step, rm -rf $(PRODUCT_OUT)/root/default.prop)

$(call add-clean-step, rm -rf $(PRODUCT_OUT)/recovery/root/default.prop)

# ************************************************

# NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST

# ************************************************