selftests/bpf: revert iter test subprog precision workaround

selftests/bpf: revert iter test subprog precision workaround

Now that precision propagation is supported fully in the presence of
subprogs, there is no need to work around iter test. Revert original
workaround.

This reverts be7dbd275dc6 ("selftests/bpf: avoid mark_all_scalars_precise() trigger in one of iter tests").

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230505043317.3629845-11-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>