nixosTests.kexec: do not use bootloader

There's no reason to use a bootloader when testing kexec, this is a feature
that reboots *directly* in the kernel, if anything, we should just direct boot the
kernel and reboots in the kernel.

A bootloader test really makes sense to test "default" systemctl kexec behavior which is already broken
because systemctl kexec will read the ESP to determine what to kexec by default.

nixos/tests/kexec.nix

@@ -8,10 +8,6 @@ import ./make-test-python.nix ({ pkgs, lib, ... }: {
     node1 = { ... }: {
       virtualisation.vlans = [ ];
       virtualisation.memorySize = 4 * 1024;
-      virtualisation.useBootLoader = true;
-      virtualisation.useEFIBoot = true;
-      boot.loader.systemd-boot.enable = true;
-      boot.loader.efi.canTouchEfiVariables = true;
     };
 
     node2 = { modulesPath, ... }: {