selftests/bpf: Fix selftests failure

The kflag is supported now for BTF_KIND_ENUM.
So remove the test which tests verifier failure
due to existence of kflag.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220607062657.3723737-1-yhs@fb.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>