api!: Remove unused config smtp_certificate_checks, deprecate old transport configs

[Hocuri]

In preparation for mt, this deprecates the old configs Config::Addr, Config::MailPw, etc. which were used to pass login data to core
and the Config::Configured* configs which I replaced by the transports table.

smtp_certificate_checks was not used by anything, so I removed it instead of deprecating.

Also, fix small bug that the configured server didn't turn up in get_info().

There are still some transport-related configs left, and we will need to discuss what to do about them:

• SentboxWatch, MvboxMove, OnlyFetchMvbox - maybe they can just stay a global setting
• ConfiguredInboxFolder, ConfiguredMvboxFolder, ConfiguredSentboxFolder, ConfiguredTrashFolder - we probably need put these into the transports table
• ConfiguredProvider
• IsChatmail
• AuthservIdCandidates - this one we can just remove