support/testing: remove leftover kernel config fragment

Commit 86d32208b62a (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>

support/testing/conf/binfmt-misc-kernel-fragment.config

@@ -1,2 +0,0 @@
-# Needed for binfmt_misc service: "Arbitrary Executable File Formats File System"
-CONFIG_BINFMT_MISC=y