Fix printing of abstract universe contexts.
Fix printing of abstract universe contexts.

Due to their representation using names, the instance was not properly
displayed.

JasonGross/coq,gares/coq,maximedenes/coq,silene/coq,ejgallego/coq,SkySkimmer/coq,JasonGross/coq,coq/coq,coq/coq,Zimmi48/coq,ejgallego/coq,silene/coq,SkySkimmer/coq,gares/coq,maximedenes/coq,Matafou/coq,SkySkimmer/coq,Matafou/coq,JasonGross/coq,gares/coq,ppedrot/coq,gares/coq,ejgallego/coq,silene/coq,gares/coq,Zimmi48/coq,Zimmi48/coq,JasonGross/coq,coq/coq,ejgallego/coq,ppedrot/coq,ppedrot/coq,maximedenes/coq,ppedrot/coq,maximedenes/coq,SkySkimmer/coq,Matafou/coq,Zimmi48/coq,ppedrot/coq,coq/coq,maximedenes/coq