drop number from cloud3-admin/ subdirectories

This will allow us to branch for Cloud 4 and then have two different branches
which are easily comparable.

However, the generated box will still have the product release number in its
name and hostname, in order to clearly distinguish between boxes corresponding
to different product releases.
And that's correct, because the appliance is still based on SUSE Cloud 3.  When we branch, `master` will be based on Cloud 4.