Tell the user explicitly about their mistakes:
* Unknown options, e.g. -list instead of -dump
or -delete instead of -remove.
* Unknown view names.
* Excess arguments.
Include the view name in `rndc nta -dump` output, for consistency with
the NTA add and remove actions.
When removing an NTA from all views, do not abort with an error if the
NTA was not found in one of the views.
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