Remove the aria-label from the site title block

[carolinan]

Description

An aria-label is added to the site title when the "Make title link to home" and the "open in new tab" options are enabled.
The purpose is to announce to screen readers that the link opens in a new tab.

The problem is that only the message "opens in a new tab" is announced to screen readers, because the aria-label replaces the link text.

There are many past discussions about the underlying problem, but I was not aware of them when I added the aria-label to the block. It is clear from these past discussions that the aria-label, even if it would include the site title in the label, is not the correct solution.
This pr removes the aria-label and restores the link text.

Testing Instructions

1. Apply the PR
2. Create a new post or page
3. Add a site title block. Enable both link settings.
4. Save, and view the front.
5. View source and confirm that the aria-label is not present for the site title link.
6. Optionally activate a screen reader and confirm that the link text is correct.

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• I've updated related schemas if appropriate.

[fabiankaegy]

This got cherry picked into the Gutenberg 12.5 release with this commit: d128390

[Mamaduka]

Backported to WP minor.