wrapper: simplify arg copying
wrapper: simplify arg copying

The "-l" processing that was hoisted up in the previous commit made
the "arg" variable effectively a constant. Replace it and the
associated "ofs" variable with inline constants.

tjt263/tmux-MacOSX-pasteboard,lembacon/tmux-MacOSX-pasteboard,ChrisJohnsen/tmux-MacOSX-pasteboard,bradparks/tmux-MacOSX-pasteboard