Cleanup previous Heptapod Rails downloads
All downloaded Heptapod Rails tarballs are kept in the cache:
$ ls -alh /var/cache/omnibus/* || /bin/true
total 790M
drwxr-xr-x 1 root root 1.7K Sep 23 19:39 .
drwxr-xr-x 1 root root 10 Sep 24 14:17 ..
-rw------- 1 root root 9.9M Sep 21 13:07 GraphicsMagick-1.3.36.tar.gz
-rw------- 1 root root 25M Sep 21 13:07 Python-3.9.9.tgz
-rw------- 1 root root 764K Sep 21 13:07 bzip2-1.0.6.tar.gz
-rw------- 1 root root 199K Sep 21 13:07 cacert-2021-09-30.pem
drwxr-xr-x 1 root root 6 Sep 21 13:08 git_cache
-rw------- 1 root root 6.8M Sep 21 13:07 gnupg-2.2.23.tar.bz2
-rw------- 1 root root 1.7M Sep 21 13:07 gpgme-1.14.0.tar.bz2
-rw------- 1 root root 50M Sep 21 13:07 grafana-7.5.15.linux-amd64.tar.gz
-rw------- 1 root root 98M Sep 22 10:55 heptapod-rails-0.33.0rc1.tar.gz
-rw------- 1 root root 98M Sep 23 19:39 heptapod-rails-0.33.0rc2.tar.gz
-rw------- 1 root root 99M Sep 21 13:08 heptapod-rails-d0d4b5e694324f385f2c93348e9f77ff207d6e87.tar.gz
-rw------- 1 root root 559K Sep 21 13:07 libassuan-2.5.3.tar.bz2
...
Up to now, in practice a given cache was used only for a couple Heptapod versions, and therefore it didn't matter so much. However, with heptapod#699 (closed), this is about to change, we'll have dozens of them.