fixed postscript in capture function by removing duplucate line

[wtjerry]

The postscript specified in postscript.py do_capture() was not valid and lead to the tested printers rejecting that command.

[jensvoid]

Thanks @wtjerry. It took seven month for someone to figure out the PS code was broken here :)

(Actually, the whole capture PS code is really bad / not generic enough because different printers require different special treatment. Need to rewrite this one day to make it work on as many devices as possible...)