incremental upgrades: complete phase four

This is what we want to do soon after incremental upgrades have been enabled by default in a Tails release.

Parent Task: #5919 (closed)

Subtasks

• #6505 (closed)
• #6575 (closed)
• #6593 (closed)
• #6513 (closed)
• #6728 (closed)

Related issues

• Blocked by #6014 (closed)

Original created by @intrigeri on 6508 (Redmine)