doc: remove release notes for release branch

doc: remove release notes for release branch

This commit does not and will not exist in main. This commit must be
redone whenever a release branch is cut (unfortunately).

Removing doc/releases is necessary to make redirects work in
ReadTheDocs. See [1], quoted:

    By default, redirects are followed only if the requested page
    doesn’t exist (404 File Not Found error), if you need to apply a
    redirect for files that exist, mark the Force redirect option. This
    option is only available on some plan levels. Please ask support if
    you need it for some reason.

After this change, URLS for /en/$release/releases will redirect to
/en/latest/releases.

[1] https://docs.readthedocs.io/en/stable/user-defined-redirects.html#features

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>