Fix CA2202: Do not dispose objects multiple times
Fix CA2202: Do not dispose objects multiple times

Nested using statements often result in this warning. The warning is
technically correct, and one way to deal with it is to combine the
using statements.

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