Remove the Breadcrumbs settings from the customizer

[enricobattocchi]

• If in the Settings we set Enable breadcrumbs for your theme to on (or the theme supports yoast-seo-breadcrumbs), the Customizer will display a "Yoast SEO Breadcrumbs" section which replicates completely the Breadcrumbs section in the Settings.
• if the same setting is off instead, the Customizer will still be displayed even if a block-based theme is used. This happens because the WPSEO_Customizer class hooks into customize_register.

The Customizer is the old way to manage settings in a sort of WYSIWYG way, but it's being phased out in favor of the much more complete options included in the site editor when using a block-based theme. We should consider either:

• deprecating the class completely
• or removing it for block-based themes which are not supposed to see a Customizer page anymore, while keeping the section for non block-based themes but with e.g. a warning inviting to use the Settings instead

[enricobattocchi]

Since the section is visible only if you have visited the settings, or you are a user so advanced to add theme support for breadcrumbs, I'd vote to deprecate the class completely

[enricobattocchi]

Decision after refinement: we should deprecate the class since people can already use the settings (and our documentation seems to refer only to those). In the future we may explore the chance of adding these and other options to the site editor.