Prevent failed attempts to override the reply-title heading in comment form

[westonruter]

Summary

This is a short-term fix to prevent attempting to integrate amp-bind with the “Leave a Reply” heading in the comment form. Because WordPress only provides a comment_form_defaults filter for the comment_form() function, and not a filter like comment_form_args to modify the actual args passed in, we cannot use the comment_form_defaults filter to inject amp-bind logic into the form.

Longer-term solutions would be to introduce the comment_form_args filter to core, or even better to not use amp-bind and instead use amp-script for this.

The effect of this PR is that the “Leave a Reply” heading will remain unchanged in Twenty Nineteen and Twenty Twenty when you enter a comment or click a “Reply” link in the comments list. In Twenty Seventeen, which does not pass any arguments to comment_form(), the heading will change from “Leave a Reply” to “Leave a Reply to John Smith” when clicking the reply link. In all themes, the “Cancel Reply” link should still appear regardless of the heading changing.

Additionally, this PR prevents the amp-bind warning message from appearing:

Default value () does not match first result (Leave a Reply) for <SPAN [text]="commentform_post_2013.replyToName ? "Leave a Reply to " + commentform_post_2013.replyToName + "" : "Leave a Reply"">. We recommend writing expressions with matching default values, but this can be safely ignored if intentional.

Fixes #2489.

Checklist

• My pull request is addressing an open issue (please create one otherwise).
• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[laurelfulford]

Thanks Weston!

I've tested this PR with Twenty Nineteen, and with the Newspack theme and our plugin that renames comment labels. In both cases, it worked like a charm -- the duplicate title no longer happened, and the custom text you can add with the Rename Comments plugin was respected 👍