Don't display the Enigmail setup wizard by default when starting Thunderbird

We did not display it before Tails 3.8 (in line with the decision made on #10436 (closed)) but Tails 3.8 displays it. It should not.

Feature Branch: bugfix/15746-hide-enigmail-config-wizard

Original created by @intrigeri on 15746 (Redmine)

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