pkg/system: rewrite IsWindowsClient() using golang.org/x/sys/windows
pkg/system: rewrite IsWindowsClient() using golang.org/x/sys/windows

Looks like we should be able to use the implementation from x/sys/windows.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

jimjag/docker,bearstech/moby,gnailuy/docker,flavio/docker,konstruktoid/docker-upstream,nalind/docker,nalind/docker,vdemeester/docker,vdemeester/docker,bearstech/moby,flavio/docker,bearstech/moby,Mokolea/docker,Ramzec/docker,trebonian/docker,mahak/docker,trebonian/docker,bearstech/moby,nalind/docker,konstruktoid/docker-upstream,moby/moby,cpuguy83/docker,Ramzec/docker,mahak/docker,gnailuy/docker,nawawi/docker,jimjag/docker,moby/moby,gnailuy/docker,flavio/docker,Ramzec/docker,mahak/docker,jimjag/docker,Mokolea/docker,moul/docker,nawawi/docker,yosifkit/docker,trebonian/docker,yosifkit/docker,thaJeztah/docker,jimjag/docker,cpuguy83/docker,trebonian/docker,moul/docker,mahak/docker,nawawi/docker,cpuguy83/docker,thaJeztah/docker,vdemeester/docker,cpuguy83/docker,Ramzec/docker,nalind/docker,yosifkit/docker,konstruktoid/docker-upstream,thaJeztah/docker,Mokolea/docker,konstruktoid/docker-upstream,thaJeztah/docker,moby/moby,moby/moby,gnailuy/docker,yosifkit/docker,moul/docker,nawawi/docker,Mokolea/docker,moul/docker,flavio/docker