nixos/amazon-image: default to 5.15 kernel

Previously, it was held back due to the ENA driver not building on the
current default (5.15). The previous commit bumps the ENA driver, which
allows 5.15 to work.

nixos/modules/virtualisation/amazon-image.nix

@@ -37,13 +37,11 @@ in
       { assertion = cfg.efi -> cfg.hvm;
         message = "EC2 instances using EFI must be HVM instances.";
       }
-      { assertion = versionOlder config.boot.kernelPackages.kernel.version "5.15";
-        message = "ENA driver fails to build with kernel >= 5.15";
+      { assertion = versionOlder config.boot.kernelPackages.kernel.version "5.17";
+        message = "ENA driver fails to build with kernel >= 5.17";
       }
     ];
 
-    boot.kernelPackages = pkgs.linuxKernel.packages.linux_5_10;
-
     boot.growPartition = cfg.hvm;
 
     fileSystems."/" = mkIf (!cfg.zfs.enable) {