[MacPorts] #58245: mpv: update config-maintainer to avoid deprecation warnings

[MacPorts]

#58245: mpv: update config-maintainer to avoid deprecation warnings
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  Reporter:  dbevans      |      Owner:  Ionic
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  mpv          |
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Comment (by dbevans):

 FYI, here are the particulars about the system that I used for testing:

 {{{
   Model Name:           Mac mini (Late 2012)
   Model Identifier:     Macmini6,1
   Processor Name:       2.5 Ghz Intel Core i5
   Graphics:             Intel HD Graphics 4000 1536 MB

   macOS 10.14.4 18E226
   Xcode 10.2 10E125 (actually using prebuilt binary built with Xcode 10.1)
 }}}

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Ticket URL: <https://trac.macports.org/ticket/58245#comment:1>
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