This is breaking the tarball build, because #128502 depends on this test
existing. After this commit, nixpkgs.tarball once again evaluates.
(cherry picked from commit 0dccbe2729efbaee995605bff8de3c83ca61860f)
The test doesn't evaluate since #125469 because Linux 5.11 got removed
as it's EOL.
As this fixes the evaluation of the test and it only removes a
declaration that was apparently forgotten, I figured that a push to
unbreak the test is fine.
(cherry picked from commit 10eab5b6b3d1d38ffd3594fa6e4be13924dafd15)
Pass the args from kernel-generic.nix's top-level to the individual
tests. Makes `nix-build -A nixosTests.kernel-generic.<attr>` and
`nix-build nixos/tests/kernel-generic.nix -A <attr>` work as expected.