We have compentent tools to bump PORTREVISION and don't need these
placeholders that serve no purpose other than to uglify the Makefile.
cad/freecad-devel and cad/openscad-devel are good recent examples
of where tools have been used to bump PORTREVISION, but there was
a residual commented PORTREVISION line prior to this commit.
Approved by: portmgr (blanket)
f4cfe9193d