nixos/release-combined: remove basic kernel tests

Arguably, breaking linux-latest should not block a release.  Also, booting
the kernel + basic sanity checking is implicitly exercised by every other
vm test.

nixos/release-combined.nix

@@ -94,8 +94,6 @@ in rec {
         (all nixos.tests.keymap.neo)
         (all nixos.tests.keymap.qwertz)
         nixos.tests.plasma5.x86_64-linux # avoid big build on i686
-        (all nixos.tests.kernel-latest)
-        (all nixos.tests.kernel-lts)
         #(all nixos.tests.lightdm)
         (all nixos.tests.login)
         (all nixos.tests.misc)