print/latex2rtf: Unbreak the option LATEX2PNG

It was broken in the run-time:
/usr/local/bin/latex2png: line 140: latex: command not found
/usr/local/bin/latex2png: line 151: xelatex: command not found
and latex2png also says in its text that it requires dvipsk.

Approved by: portmgr (unbreak)