Related to #51769 and #51819

Part of #41479.

Dependent upon #51770, #51819, and #50927 being merged into trunk.

What problem does this address?

The Fonts API will be dead code once the Font Library is merged into trunk, as it will not load into memory.

What is your proposed solution?

Once Font Library, Font Face, and #51819 are all merged into trunk, then:

1. Delete the entire /lib/experimental/fonts-api/ folder.
2. Delete the require lines for each of those files in lib/load.php.