Don't remove paging params from arg table, hide them

This allows us to add pagination configs after the fact and
still remain backwards compatible with users performing their own
pagination.

The new logic is to support the manual, per-service pagination
arguments, but not document them.  If we see that the user has provided
manual pagination arguments, we automatically switch `--no-paginate`
on.

This keeps pagination backwards compatible.  If a user was manually
paginating responses:

    aws service op --next-marker foo

And we add pagination configs to the service, then the previous command
will still work because we'll detect the --next-marker argument
corresponds to a pagination arg, we'll instruct the CLI to not auto
paginate, and the user will have the same behavior.

The tab completion tests were also failing because of this change.
This also includes a fix so that we don't tab complete undocumented
operations/params.