samples/bpf: remove obsolete tracing related tests

samples/bpf: remove obsolete tracing related tests

The samples/bpf has become outdated and often does not follow up with
the latest. This commit removes obsolete tracing-related tests.

Specifically, 'test_overhead' is duplicate with selftests (and bench),
and 'test_override_return', 'test_probe_write_user' tests are obsolete
since they have been replaced by kprobe_multi_override and probe_user
from selftests respectively.

The following files are removed:
- test_overhead: tests the overhead of BPF programs with task_rename,
  now covered by selftests and benchmark tests (rename-*). [1]

- test_override_return: tests the return override functionality, now
  handled by kprobe_multi_override in selftests.

- test_probe_write_user: tests the probe_write_user functionality,
  now replaced by the probe_user test in selftests.

This cleanup will help to streamline the testing framework by removing
redundant tests.

[1]: https://patchwork.kernel.org/cover/13759916

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20241011044847.51584-5-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>