Update changelog/ for new version of calens

We've reworked calens[1] a bit, the changelog/releases file is not
needed any more. Insteady, the release date is stored in the dir name
which contains the changelog entries.

[1] https://github.com/restic/calens

changelog/releases

@@ -1,14 +0,0 @@
-# This file lists all versions for the changelog. Each line consists of the
-# version string, followed by an optional release date.
-# 
-# The resulting changelog generated by `calens` will list all versions in
-# exactly this order.
-0.8.2
-0.8.1 2017-12-27
-0.8.0 2017-11-26
-0.7.3 2017-09-20
-0.7.2 2017-09-13
-0.7.1 2017-07-22
-0.7.0 2017-07-01
-0.6.1 2017-06-01
-0.6.0 2017-05-29