helm: remove mention of helm.sh clean

tests/scripts/helm.sh clean is not implemented.

So  remove frpom the script's help text
and from the development guilde

Signed-off-by: Michael Adam <obnox@samba.org>

Documentation/Contributing/development-environment.md

@@ -50,7 +50,6 @@ minikube delete
 Use [helm.sh](https://github.com/rook/rook/blob/master/tests/scripts/helm.sh) to install Helm and set up Rook charts defined under `_output/charts` (generated by build):
 
 - To install and set up Helm charts for Rook run `tests/scripts/helm.sh up`.
-- To clean up `tests/scripts/helm.sh clean`.
 
 !!! note
     These helper scripts depend on some artifacts under the `_output/` directory generated during build time.

tests/scripts/helm.sh

@@ -46,5 +46,4 @@ case "${1:-}" in
     *)
         echo "usage:" >&2
         echo "  $0 up" >&2
-        echo "  $0 clean" >&2
 esac