BIND 10 #1820: remove DNSService::addServer()

[BIND 10 Development]

#1820: remove DNSService::addServer()
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  medium        |                    Milestone:  Next-
           Component:  Unclassified  |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 Since we switched to FD-based creation we don't use these methods
 in our system any more.  Keeping such effectively dead code increases
 maintenance cost and decreases readability, so I propose removing
 them.

 From a quick look, one of the constructors and some other methods in
 the implementation class can (and should) also be removed.

 (Even if we have some expectation that we may reuse them in an
 unforeseen future, we could do that any time when the plan is actually
 realized by retrieving the old code from the repository)

 See also the related discussion in #1784.

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Ticket URL: <http://bind10.isc.org/ticket/1820>
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