This removes the description of the ephemeral containers API from the
concepts section of the website. Most (all?) concepts don't have a
detailed description of their API in concepts. We added it for the
initial release of ephemeral containers because using the raw API was
the only way to add an ephemeral container.
This description of the API is no longer correct. Since it's now easy to
add an ephemeral container using `kubectl debug`, and this is too much
detail for a concepts section, we should remove the API description
entirely.
ede985dccd