WooCommerce Brands: Revert to Product Category support only.

[sybrew]

WooCommerce 9.4 introduced the "Brands" taxonomy for testing. WooCommerce 9.6 enabled this taxonomy for all sites.

The "Brands" taxonomy supersedes the "Product Categories" taxonomy for TSF's breadcrumb generation. This affects established sites that have yet to embrace Brands: The breadcrumb output now misses the Product Category terms and instead uses the Brands terms (if any).

We must consider changing the preferred taxonomy behavior as before. At least, until we can get #668 going, with which users should be able to select their preferred taxonomy.

[sybrew]

We should add a toggle for this, as changing this behavior may negatively impact new WooCommerce sites.

This toggle must be migrated later to #668, which may be annoying.