[3.4] RFC: Apply the new development strategy to the Update channel infos

According to our new development strategy:
http://developer.joomla.org/news/586-joomla-development-strategy.html#version_numbering

We don't use LTS or STS anymore.

@roland-d can you have a look into this as the initial PR was yours? Thanks :+1: 

See also https://github.com/joomla/joomla-cms/pull/3681