Unhook _block_template_render_title_tag

[aristath]

Description

Fixes #34106

When gutenberg_render_title_tag was backported to WP as _block_template_render_title_tag, we should have unhooked it along with _wp_render_title_tag.
That was not done, and as a result we have 2 <title> elements in the head.
Additional information is available in the ticket.

This PR simply unhooks _block_template_render_title_tag to fix the issue.

How has this been tested?

Tested with a block theme, creating a template override for a single page.

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).

[gziolo]

Makes sense 👍🏻