remove checker/Makefile
remove checker/Makefile

 This historical Makefile was used during the development of coqcheck,
 but was unused since then : the checker is built via Coq's main Makefile.
 So let's remove this one to avoid any risk of confusion.

silene/coq,Lionel-Rieg/coq,ejgallego/coq,Matafou/coq,Ptival/coq,Lionel-Rieg/coq,gares/coq,ejgallego/coq,gares/coq,maximedenes/coq,Ptival/coq,ejgallego/coq,silene/coq,JasonGross/coq,coq/coq,Zimmi48/coq,maximedenes/coq,ejgallego/coq,Zimmi48/coq,letouzey/coq-wip,william-lawvere/coq,Zimmi48/coq,ppedrot/coq,letouzey/coq-wip,gares/coq,letouzey/coq-wip,coq/coq,amintimany/coq,maximedenes/coq,SkySkimmer/coq,maximedenes/coq,coq/coq,william-lawvere/coq,Matafou/coq,amintimany/coq,JasonGross/coq,JasonGross/coq,SkySkimmer/coq,letouzey/coq-wip,ppedrot/coq,amintimany/coq,letouzey/coq-wip,maximedenes/coq,Matafou/coq,coq/coq,ppedrot/coq,ppedrot/coq,SkySkimmer/coq,JasonGross/coq,william-lawvere/coq,silene/coq,ppedrot/coq,SkySkimmer/coq,Zimmi48/coq,gares/coq,gares/coq,Lionel-Rieg/coq,Ptival/coq