Do not include CellBroadcastLegacy for Go devices

CellBroadcastLegacy app is for migrating data from pre-mainline world.
Go devices do not take mainline module, thus excluding this apk
from build. Otherwise, both CellBroadcastLegacy app and
CellBroadcastAppPlatform will have the same package name
com.android.cellbroadcastreceiver

Bug: 157702986
Test: build go target:  walleye_svelte-userdebug
Change-Id: I254a8af334580b79ffdbc9e8bfa95b23500f507e

CleanSpec.mk

@@ -713,6 +713,9 @@ $(call add-clean-step, rm -rf $(PRODUCT_OUT)/vendor/etc/vintf/manifest/android.h
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/apex/com.android.cellbroadcast.apex)
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/apex/com.android.cellbroadcast)
 
+# Remove CellBroadcastLegacyApp for Go devices
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/priv-app/CellBroadcastLegacyApp)
+
 # Remove MediaProvider after moving into APEX
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/priv-app/MediaProvider)