Remove unneeded ESSP options from ecctl

## Overview
There are a few stray references to ESSP, which has been decommissioned. A couple of examples:

https://github.com/elastic/ecctl/blob/master/pkg/ecctl/init.go#L103
https://github.com/elastic/ecctl/blob/master/pkg/ecctl/init.go#L122
https://github.com/elastic/ecctl/blob/master/pkg/ecctl/init.go#L399
etc.

We should remove the ESSP pathway because it is no longer relevant.