Update the SMTP (PHPMailer) adapter for the new mail API; remove "encoding" and "mailer"
- Update to the new "$message" API.
- Remove "encoding". I believe "base64" is always the best value for this since we stopped seeing issues once we changed the default.
- Remove "mailer". This is a legacy option that makes little sense given how configuration now works.
- Rename to "SMTP". This doesn't affect users anymore since this mailer has been configured as smtp for about a year.
- This does NOT add a timeout since the SMTP code is inside PHPMailer (see T12404).
Test Plan: Sent messages with many mail features via GMail SMTP and SendGrid SMTP.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D19961