Removed Thunderbird release symlinks for dead branches on FTP

Since the Thunderbird 2.0 days we’ve had “latest-X.Y” symlinks on FTP for all major versions of Thunderbird. With rapid release, this has quickly caused an explosion in the number of them, cluttering things up (as Firefox have already realised and taken action).

In bug 697050 I have just removed all of the ones for the dead branches (2.0, 3.0), and also the ones for all rapid releases (5.0, 6.0, 7.0, 8.0). From now on, there will be no new branch based symlinks, simply a “latest” symlink that points to the latest rapid release.