Some changes for external call transfer, REF 16135

- Add Require=replaces, user=phone into Refer-To header field
- Remove to-tag, from-tag, from Refer-To:replaces

Note that the changes only make the test move forward a bit. But external transfer
as a feature still does NOT work after this commit. The reason to accept this partial
change is that it has been pushed into the customer's git repo and we have to keep
the code synchronised.