[MacPorts] #56110: Travis: skip building ports from the obsolete PortGroup

[MacPorts]

#56110: Travis: skip building ports from the obsolete PortGroup
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  Reporter:  mojca          |      Owner:  l2dy
      Type:  defect         |     Status:  new
  Priority:  Low            |  Milestone:
 Component:  buildbot/mpbb  |    Version:
Resolution:                 |   Keywords:
      Port:                 |
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Comment (by mojca):

 Fix `mpbb`

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Ticket URL: <https://trac.macports.org/ticket/56110#comment:2>
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