[MacPorts] #30201: Drop +postgres83 variant from mediawiki

[MacPorts]

#30201: Drop +postgres83 variant from mediawiki
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 Reporter:  chad@…                  |       Owner:  blb@…           
     Type:  defect                  |      Status:  new             
 Priority:  Normal                  |   Milestone:                  
Component:  ports                   |     Version:  1.9.2           
 Keywords:                          |        Port:  mediawiki       
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Comment(by blb@…):

 Note that the versioned database variants were deprecated a while ago in
 favor of just 'mysql' and 'postgresql' (#20854) since the specific version
 is picked when php5-mysql or php5-postgresql is installed.  This of course
 means that there could be issues if an unsupported postgresql version is
 used for php5-postgresql, but I'm not sure of an easy way to test for
 that.

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Ticket URL: <https://trac.macports.org/ticket/30201#comment:2>
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