selftests/bpf: Remove bpf_assert_eq-like macros.

Since the last user was converted to bpf_cmp, remove bpf_assert_eq/ne/... macros.

__bpf_assert_op() macro is kept for experiments, since it's slightly more efficient
than bpf_assert(bpf_cmp_unlikely()) until LLVM is fixed.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20231226191148.48536-5-alexei.starovoitov@gmail.com