[1.7.x] Added a missing word in a skip message

Backport of 8b6cb9d0dd from master
[1.7.x] Removed sentence from docs about migrate prompting to add a superuser.

Backport of 21a9e8adf0 from master
[1.7.x] Fixed #23391 -- Removed an erroneous backtip from the form's documentation.

Thanks to Trac alias nessita for the report.

Backport of ab9c886459 from master