Delete pending release confirmation if the tag is removed

[dd32]

When a plugin has Release Confirmations enabled, if the tag is deleted before the request is confirmed, the release remains in the plugin admin showing as "release confirmation needed".

When a tag is removed, it should remove any pending confirmations.

Potentially, the release should remain in the list, just marked as 'deleted' or 'removed'.

Additionally, it would be beneficial if there was an Admin UI for plugin reviewers to remove/block/disable/something pending confirmations for plugins.
This would be used in the event that either

• A bug occurs (such as this tickets cause) or
• In the event that a plugin author were to contact the team with a "Don't release that!!" - there needs to be some way to ignore/discard the pending release.

[dd32]

Additionally, it would be beneficial if there was an Admin UI for plugin reviewers to remove/block/disable/something pending confirmations for plugins.

This was implemented via [12813], plugin authors also have access to it.

[dd32]

In 13709:

Plugin Directory: SVN: Watch for Tag deletions, such that we can properly handle cases when a tag is deleted.

See #3263, #5900.

[dd32]

In 13711:

Plugin Direcrory: When Release Confirmation is enabled, and a tag for a non-confirmed release is deleted, remove the release.

Fixes #5900.

[dd32]

In 13959:

Plugin Directory: Release Confirmation: Remove releases for deleted tags earlier.

When a SVN tag is removed the relevant release is deleted [13711], but that only applied when release confirmation was enabled.

As of the changes in #7696 releases now exist even if release confiramtion isn't enabled, as such as should always remove any release meta for any non-explicitely-confirmed releases.

This also has the effect of resolving an edge-case where the deleted tag is present within trunk/readme.txt as the Stable Tag but the release was discarded/not-confirmed, in that case $stable_tag would be set to the fallback value of 'trunk' for the SVN import and ultimately release confirmation would reject the import (as trunk is not currently valid for that scenario).
That would cause the release NOT to be deleted, although the tag was. Replacing the tag with the corrected data would not re-trigger the confirmation process if the release was previously discarded.

See #7696, #5900.