onboarding: Use delivery_email in "new login" notifications.
onboarding: Use delivery_email in "new login" notifications.

Since we implemented EMAIL_ADDRESS_VISIBILITY_ADMINS, the intent is
that `delivery_only` should be used for accessing a user's actual
email address; with `email` used only in the Zulip API where we
haven't migrated to interacting with other users by ID.

This fixes a place we neglected to migrate.

timabbott/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,timabbott/zulip,timabbott/zulip,timabbott/zulip,synicalsyntax/zulip,timabbott/zulip,shubhamdhama/zulip,showell/zulip,showell/zulip,timabbott/zulip,shubhamdhama/zulip,shubhamdhama/zulip,synicalsyntax/zulip,showell/zulip,eeshangarg/zulip,andersk/zulip,showell/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,zulip/zulip,hackerkid/zulip,hackerkid/zulip,rht/zulip,punchagan/zulip,eeshangarg/zulip,shubhamdhama/zulip,andersk/zulip,shubhamdhama/zulip,synicalsyntax/zulip,synicalsyntax/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,showell/zulip,rht/zulip,brainwane/zulip,punchagan/zulip,brainwane/zulip,eeshangarg/zulip,punchagan/zulip,andersk/zulip,kou/zulip,andersk/zulip,kou/zulip,andersk/zulip,rht/zulip,synicalsyntax/zulip,brainwane/zulip,showell/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,hackerkid/zulip,hackerkid/zulip,kou/zulip,shubhamdhama/zulip,punchagan/zulip,synicalsyntax/zulip,timabbott/zulip,zulip/zulip,shubhamdhama/zulip,andersk/zulip,rht/zulip,kou/zulip,kou/zulip,zulip/zulip,kou/zulip,showell/zulip,eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,brainwane/zulip,kou/zulip,rht/zulip,brainwane/zulip,synicalsyntax/zulip,hackerkid/zulip,eeshangarg/zulip,brainwane/zulip