Don't generate unused rewrite rules for alerts post type

[ocean90]

register_post_type() generates rewrite rules by default even if the post type isn't public. Two avoid this we can pass 'rewrite' => false.

Currently the rewrite_rules options also contains these rules:

  'wp_stream_alerts/[^/]+/attachment/([^/]+)/?$' => 'index.php?attachment=$matches[1]',
  'wp_stream_alerts/[^/]+/attachment/([^/]+)/trackback/?$' => 'index.php?attachment=$matches[1]&tb=1',
  'wp_stream_alerts/[^/]+/attachment/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$' => 'index.php?attachment=$matches[1]&feed=$matches[2]',
  'wp_stream_alerts/[^/]+/attachment/([^/]+)/(feed|rdf|rss|rss2|atom)/?$' => 'index.php?attachment=$matches[1]&feed=$matches[2]',
  'wp_stream_alerts/[^/]+/attachment/([^/]+)/comment-page-([0-9]{1,})/?$' => 'index.php?attachment=$matches[1]&cpage=$matches[2]',
  'wp_stream_alerts/[^/]+/attachment/([^/]+)/embed/?$' => 'index.php?attachment=$matches[1]&embed=true',
  'wp_stream_alerts/([^/]+)/embed/?$' => 'index.php?wp_stream_alerts=$matches[1]&embed=true',
  'wp_stream_alerts/([^/]+)/trackback/?$' => 'index.php?wp_stream_alerts=$matches[1]&tb=1',
  'wp_stream_alerts/([^/]+)/page/?([0-9]{1,})/?$' => 'index.php?wp_stream_alerts=$matches[1]&paged=$matches[2]',
  'wp_stream_alerts/([^/]+)/comment-page-([0-9]{1,})/?$' => 'index.php?wp_stream_alerts=$matches[1]&cpage=$matches[2]',
  'wp_stream_alerts/([^/]+)(?:/([0-9]+))?/?$' => 'index.php?wp_stream_alerts=$matches[1]&page=$matches[2]',
  'wp_stream_alerts/[^/]+/([^/]+)/?$' => 'index.php?attachment=$matches[1]',
  'wp_stream_alerts/[^/]+/([^/]+)/trackback/?$' => 'index.php?attachment=$matches[1]&tb=1',
  'wp_stream_alerts/[^/]+/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$' => 'index.php?attachment=$matches[1]&feed=$matches[2]',
  'wp_stream_alerts/[^/]+/([^/]+)/(feed|rdf|rss|rss2|atom)/?$' => 'index.php?attachment=$matches[1]&feed=$matches[2]',
  'wp_stream_alerts/[^/]+/([^/]+)/comment-page-([0-9]{1,})/?$' => 'index.php?attachment=$matches[1]&cpage=$matches[2]',
  'wp_stream_alerts/[^/]+/([^/]+)/embed/?$' => 'index.php?attachment=$matches[1]&embed=true',

With this change the above rules will be removed.

Checklist

• [ ] Project documentation has been updated to reflect the changes in this pull request, if applicable.
• [x] I have tested the changes in the local development environment (see contributing.md).
• [ ] I have added phpunit tests.

Release Changelog

• Fix: Don't generate unused rewrite rules for alerts post type.

Release Checklist

• [ ] This pull request is to the master branch.
• [ ] Release version follows semantic versioning. Does it include breaking changes?
• [ ] Update changelog in readme.txt.
• [ ] Bump version in stream.php.
• [ ] Bump Stable tag in readme.txt.
• [ ] Bump version in classes/class-plugin.php.
• [ ] Draft a release on GitHub.

Change [ ] to [x] to mark the items as done.