Rethink our patches with Thunderbird 60

TB 60 comes with improvements related to protocols vs. security.

See screenshots when trying to validate a configuration with a cleartext SMTP server as discovered by the config wizard.

It seems it might be time to re-evaluate the Tails-specific patches.

Parent Task: #6156

Original created by @CyrilBrulebois on 15788 (Redmine)

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