The samples/bpf has become outdated and often does not follow up with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since they have been replaced by kprobe_multi_override and probe_user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>

The existing tracing programs have been developed for a considerable
period of time and, as a result, do not properly incorporate the
features of the current libbpf, such as CO-RE. This is evident in
frequent usage of functions like PT_REGS* and the persistence of "hack"
methods using underscore-style bpf_probe_read_kernel from the past.

These programs are far behind the current level of libbpf and can
potentially confuse users. Therefore, this commit aims to convert the
outdated BPF programs to be more CO-RE centric.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20230818090119.477441-6-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This commit changes the _kern suffix to .bpf with the BPF test programs.
With this modification, test programs will inherit the benefit of the
new CLANG-BPF compile target.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20230115071613.125791-11-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>