Commit 86d32208b6 (support/testing/tests/init/test_systemd.py: use
downloaded kernel) stopped building a custom kernel for the systemd
tests, but forgot to drop the associated kernel config fragment.
That fragment is now not used in any test case, so we can drop it.
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
0627cb0e8a