[MacPorts] #47315: simplify Makefile for doc

[MacPorts]

#47315: simplify Makefile for doc
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 Reporter:  lists@…      |      Owner:  markd@…
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  guide        |    Version:  2.3.3
 Keywords:  haspatch     |       Port:
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 this doesn't eliminate the horrible sed like I promised, but this does
 simplify and reduce duplicate effort.

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Ticket URL: <https://trac.macports.org/ticket/47315>
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