Update the docs around alpha fields & deprecating
Update the docs around alpha fields & deprecating

Fix some wording.

Remove the demand for validation to fail.  It also says to clearthose
fields, which more closely models non-existent fields.

Change the tombstone (proposed - nobody is using this yet, obviously).
This format matches what gengo uses for other tags.

kubernetes/community,pwittrock/community,kubernetes/community,pwittrock/community,bgrant0607/community,bgrant0607/community,kubernetes/community