[MacPorts] #41518: libpcl: update to 1.7.1; simplify portgroup usage

[MacPorts]

#41518: libpcl: update to 1.7.1; simplify portgroup usage
--------------------------+------------------------
 Reporter:  ryandesign@…  |      Owner:  luminans@…
     Type:  update        |     Status:  new
 Priority:  Normal        |  Milestone:
Component:  ports         |    Version:  2.2.99
 Keywords:  haspatch      |       Port:  libpcl
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 This patch updates libpcl to 1.7.1. It builds fine on Mountain Lion. It
 does not fix the build failure on Mavericks reported in #40760.

 I simplified how the github-1.0 and active_variants-1.1 portgroups are
 used, removing many now-unnecessary lines from the portfile. This also
 switches to the tar.gz file, which is smaller than the zip file the port
 was using before.

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Ticket URL: <https://trac.macports.org/ticket/41518>
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