Fix clean InProcessTethering fail problem

CleanSpec only respect root of a git project.
Remove packages/Tethering/CldanSpec.mk because it never
be read.

Bug: 144320246
Test: manual build InProcessTethering and observed it is removed
      after adding new clean step.

Change-Id: I58750e4a1fe11018d83da1ebf828d1b3134ec765
diff --git a/CleanSpec.mk b/CleanSpec.mk
index b84e715..0b7ea28 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -259,6 +259,7 @@
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/framework/service-statsd.jar)
 $(call add-clean-step, rm -rf $(SOONG_OUT_DIR)/.intermediates/frameworks/base/libincremental_aidl-cpp-source/)
 $(call add-clean-step, rm -rf $(SOONG_OUT_DIR)/.intermediates/frameworks/base/libincremental_manager_aidl-cpp-source/)
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/priv-app/InProcessTethering)
 # ******************************************************************
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST ABOVE THIS BANNER
 # ******************************************************************