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.
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.
