Upgrade/Install: Unlink the logo on the installation and config setup screens.

This allows for a natural tab order during installation, without negatively impacting users who use the keyboard for navigation, those who use a screen reader, or those who use neither.

Props lwill, afercia, audrasjb.

Fixes #47759
Built from https://develop.svn.wordpress.org/trunk@47746


git-svn-id: https://core.svn.wordpress.org/trunk@47522 1a063a9b-81f0-0310-95a4-ce76da25c4cd