clasp-common-lisp: use ninjaFlags instead of explicitly setting buildPhase and installPhase

pkgs/development/compilers/clasp/default.nix

···
     libclang
   ];
 
+  ninjaFlags = [ "-C" "build" ];
+
   postUnpack = lib.concatStringsSep "\n" (builtins.map unpackDependency dependencies);
 
   configurePhase = ''
···
       --bin-path=$out/bin \
       --lib-path=$out/lib \
       --share-path=$out/share
-  '';
-
-  buildPhase = ''
-    ninja -C build
-  '';
-
-  installPhase = ''
-    ninja -C build install
   '';
 
   meta = {