* Delete previous plans on autoplan or atlantis plan
When using non-default workspaces, plans are stored
in pr-and-workspace-specific directories.
If a PR is subsequently updated it might happen that
some of the plans are no longer relevant with regards
to the latest changes.
This change ensures that plans are always deleted
when a generic plan is triggered either by autoplan
or by a "atlantis plan" command.
NB Plans are not cleaned up when specific projects are
planned explicitly with "atlantis plan -p/-d/-w".
* Use DeleteLockCommand to delete locks and workdirs
containing previous plans
Co-authored-by: giuli007 <giuglioz@gmail.com>