Remove the old root feed files

[nacin]

These files can all go:

• wp-feed.php
• wp-rss2.php
• wp-rss.php
• wp-atom.php
• wp-commentsrss2.php
• wp-rdf.php

We can keep them in the rewrite rules (in compressed form) and then catch them in canonical, and continue to redirect them there.

Additionally, we will not add these files to $_old_files, so they won't be removed on upgrade. Of course, they are safe to remove, but it'll minimize breakage of lame use of these files.

See also #4967, the EOL of RSS 0.92 and RDF.

[nacin]

In [18540]:

Remove the old root feed files. Bump the db version so rewrite rules can regenerate. Don't add these files to old_files to leave them on existing installs. fixes #18384.

[westi]

In [18715]:

Escape the dot so that it only matches dot any not any character in the old feed files redirect.
Bump the db version so the rules regenerate.
See #18384