X.A.DynamicWorkspaces: Remove duplicates when melding
X.A.DynamicWorkspaces: Remove duplicates when melding

When removing a workspace and distributing its windows, it's important
to remove any duplicates that may be there due to, for example, usage of
X.A.CopyWindow.  X will only draw one of these window, leading to some
artifacts.

Related: https://github.com/xmonad/xmonad-contrib/issues/565

Co-authored-by: Tomas Janousek <1c3f704cb51e403ca868437e82c98b13fd6cbd4a@nomi.cz>

xmonad/xmonad-contrib,xmonad/xmonad-contrib