Delete fexit_noreturns.c files and migrate the cases into
tracing_failure.c files.
The result:
$ tools/testing/selftests/bpf/test_progs -t tracing_failure/fexit_noreturns
#467/4 tracing_failure/fexit_noreturns:OK
#467 tracing_failure:OK
Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED
Signed-off-by: KaFai Wan <kafai.wan@xxxxxxxxx>