Remove duplicate `cli` alias

Pull request #388 added a `core-cli` command which fires up a Boris shell. It has a `cli` alias. But `cli` is already aliased to `config-list`.

    Slate ~/Sites/abweb.test/www> d7 | grep cli
     core-cli (cli, php)   Open an interactive shell on a Drupal site.              
     config-list (cli)     List config names by prefix.                             
     sql-cli (sqlc)        Open a SQL command-line interface using Drupal's     
     
The commit in this PR simply removes the `cli` alias from `core-cli`. `config-list` was there first, after all, and IMO the other alias of `php` is almost as memorable.