Remove API from required installs for debian.

Debian doesn't appear to have salt-api installable, and when I try to install I see:

```sh
 * INFO: Running install_debian_check_services()
 * DEBUG: Checking if service salt-minion is enabled
 * DEBUG: Service salt-minion is enabled
 * DEBUG: Checking if service salt-master is enabled
 * DEBUG: Service salt-master is enabled
 * DEBUG: Checking if service salt-api is enabled
 * DEBUG: Service salt-api is NOT enabled
 * ERROR: Failed to run install_debian_check_services()!!!
 * DEBUG: Removing the logging pipe /tmp/bootstrap-salt.logpipe
```