tests/boot: Remove unused store contents

nixos/tests/boot.nix

···
       modules =
         [ ../modules/installer/cd-dvd/installation-cd-minimal.nix
           ../modules/testing/test-instrumentation.nix
-          { key = "serial";
-            boot.loader.grub.timeout = mkOverride 0 0;
-
-            # The test cannot access the network, so any sources we
-            # need must be included in the ISO.
-            isoImage.storeContents =
-              [ pkgs.glibcLocales
-                pkgs.sudo
-                pkgs.docbook5
-                pkgs.docbook5_xsl
-                pkgs.grub
-                pkgs.perlPackages.XMLLibXML
-                pkgs.unionfs-fuse
-                pkgs.gummiboot
-              ];
-          }
+          { key = "serial"; }
         ];
     }).config.system.build.isoImage;