remove duplicate code in XpsExporter
remove duplicate code in XpsExporter

NilesDavis/oxyplot,jeremyiverson/oxyplot,as-zhuravlev/oxyplot_wpf_fork,HermanEldering/oxyplot,ze-pequeno/oxyplot,svendu/oxyplot,freudenthal/oxyplot,TheAlmightyBob/oxyplot,bbqchickenrobot/oxyplot,svendu/oxyplot,Rustemt/oxyplot,shoelzer/oxyplot,DotNetDoctor/oxyplot,objorke/oxyplot,sevoku/oxyplot,lynxkor/oxyplot,Mitch-Connor/oxyplot,mattleibow/oxyplot,Isolocis/oxyplot,Mitch-Connor/oxyplot,Sbosanquet/oxyplot,Rustemt/oxyplot,H2ONaCl/oxyplot,DotNetDoctor/oxyplot,GeertvanHorrik/oxyplot,objorke/oxyplot,freudenthal/oxyplot,Sbosanquet/oxyplot,GeertvanHorrik/oxyplot,as-zhuravlev/oxyplot_wpf_fork,shoelzer/oxyplot,jeremyiverson/oxyplot,br111an/oxyplot,objorke/oxyplot,sevoku/oxyplot,BRER-TECH/oxyplot,H2ONaCl/oxyplot,GeertvanHorrik/oxyplot,as-zhuravlev/oxyplot_wpf_fork,Jofta/oxyplot,TheAlmightyBob/oxyplot,freudenthal/oxyplot,HermanEldering/oxyplot,Mitch-Connor/oxyplot,Rustemt/oxyplot,br111an/oxyplot,br111an/oxyplot,olegtarasov/oxyplot,shoelzer/oxyplot,mattleibow/oxyplot,bbqchickenrobot/oxyplot,Jonarw/oxyplot,BRER-TECH/oxyplot,Sbosanquet/oxyplot,H2ONaCl/oxyplot,olegtarasov/oxyplot,oxyplot/oxyplot,Kaplas80/oxyplot,jeremyiverson/oxyplot,Kaplas80/oxyplot,svendu/oxyplot,zur003/oxyplot,bbqchickenrobot/oxyplot,lynxkor/oxyplot,lynxkor/oxyplot,TheAlmightyBob/oxyplot