This parameter is somewhat useful, and adding this also fixes a
regression where purge-old-deployments would crash since the changes
around c5580607a7 because of
inconsistent supported args lists.
This commit removes redundant yarn cache by removing the old
version directories, i.e. All the directory under `~/.cache/yarn`
except `~/.cache/yarn/v6` (current version directory).
Fixes#15964.
Anders Kaseorg
Tim Abbott
Robert Imschweiler
Riken Shah