netsurf-buildsystem: move to by-name

pkgs/applications/networking/browsers/netsurf/default.nix

···
 
     browser = callPackage ./browser.nix { };
 
-    buildsystem = callPackage ./buildsystem.nix { };
+    buildsystem = pkgs.netsurf-buildsystem;
     libcss = callPackage ./libcss.nix { };
     libdom = callPackage ./libdom.nix { };
     libhubbub = callPackage ./libhubbub.nix { };