[MacPorts] #47315: simplify Makefile for doc

#47315: simplify Makefile for doc -------------------------+--------------------- Reporter: lists@… | Owner: markd@… Type: enhancement | Status: new Priority: Normal | Milestone: Component: guide | Version: 2.3.3 Keywords: haspatch | Port: -------------------------+--------------------- this doesn't eliminate the horrible sed like I promised, but this does simplify and reduce duplicate effort. -- Ticket URL: <https://trac.macports.org/ticket/47315> MacPorts <https://www.macports.org/> Ports system for OS X