AMP author template overriding the theme

Seems that even if you place a `amp/meta-author.php` template in your theme, the CAP template takes precedence. Ideally, the hierarchy should be:

Theme amp directory
CAP plugin template
AMP plugin template

This is easily fixed by unhooking the actions in `cap_add_amp_actions` but ideally it should function as described above.

Start by tracing the cap_add_amp_actions hook and how amp/meta-author.php is resolved when a theme provides it. Verify the current precedence, then confirm that the theme AMP template takes precedence over the CAP plugin template and the AMP plugin template.

Written by the indexing model from the issue text.