[MacPorts] #55459: qgis3: Don't hardcode /Applications/MacPorts

[MacPorts]

#55459: qgis3: Don't hardcode /Applications/MacPorts
------------------------+--------------------
 Reporter:  ryandesign  |      Owner:  Veence
     Type:  defect      |     Status:  new
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:
 Keywords:  haspatch    |       Port:  qgis3
------------------------+--------------------
 The qgis3 portfile says:

 {{{
 post-destroot {
     # qgis_bench app doesn’t link properly. Who uses this anyway????
     system -W
 ${destroot}/Applications/MacPorts/QGIS.app/Contents/MacOS/bin "rm -rf
 qgis_bench.app"
 }
 }}}

 You shouldn't call out to `system` for functionality already available in
 MacPorts (MacPorts has the functionality to delete files); and you
 shouldn't assume the applications are in /Applications/MacPorts (the user
 can configure MacPorts to put them somewhere else).

 To fix both issues, please change that `system` command to:

 {{{
     delete
 ${destroot}${applications_dir}/QGIS.app/Contents/MacOS/bin/qgis_bench.app
 }}}

--
Ticket URL: <https://trac.macports.org/ticket/55459>
MacPorts <https://www.macports.org/>
Ports system for macOS