fix(sms): Use the real email sender when sending via MockNexmo
fix(sms): Use the real email sender when sending via MockNexmo

We were using a made up sender, which caused our email provider
to drop the messages on the ground when testing on fxa-ci. Messages
were reported as delivered, but never seen again.

eoger/fxa-auth-server,mozilla/fxa-auth-server,mozilla/fxa-auth-server,mozilla/fxa-auth-server,eoger/fxa-auth-server,eoger/fxa-auth-server,eoger/fxa-auth-server,mozilla/fxa-auth-server