selftests/bpf: Migrate fexit_noreturns case into tracing_failure test suite

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@linux.dev>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250724151454.499040-5-kafai.wan@linux.dev


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