pdfdiff: deprecate phases

pkgs/applications/misc/pdfdiff/default.nix

···
 
   buildInputs = [  pythonPackages.wrapPython ];
 
+  dontConfigure = true;
+  dontBuild = true;
   doCheck = false;
-
-  phases = [ "unpackPhase" "patchPhase" "installPhase" ];
 
   unpackPhase = "cp $src pdfdiff.py";