Update accessibility-ready keyword when uploading an update

[grapplerulrich]

The accessibility-ready keyword should be automatically be removed from the trac ticket if it is removed from the styles.css.

The change will most likely need to made in WPORG_Themes_Upload::prepare_trac_ticket()`

[joedolson]

Yes, that would be lovely! :)

[grapplerulrich]

I think this could be solved with the following code in https://meta.trac.wordpress.org/browser/sites/trunk/wordpress.org/public_html/wp-content/plugins/theme-directory/class-wporg-themes-upload.php#L616

<?php
$new_ally_tag = ! isset( $this->theme_post->tags_input['accessibility-ready'] ) && isset( $this->trac_ticket->keywords['accessibility-ready'] );
if ( $this->trac_ticket->priority == 'theme update' && ! new_ally_tag  ) {

[ocean90]

In 5282:

Theme Directory: Update keywords when uploading an update.

This ensures that the accessibility-ready keyword gets removed if the tag gets removed from the styles.css.
Also remove the comma for multiple keywords.

Props grapplerulrich.
Fixes #1749.