vsftp: fix password envs

The password ENV is duplicated in two places, causing the default password to be "dev" instead of "application":
- https://github.com/webdevops/Dockerfile/blob/develop/docker/vsftp/latest/conf/provision/roles/webdevops-vsftp/defaults/main.yml#L10
- https://github.com/webdevops/Dockerfile/blob/develop/docker/vsftp/latest/Dockerfile#L17
