dd: skip two tests without "printf" feature

[cakebaker]

When running cargo test --features "dd" --no-default-features the compiler shows two errors like:

error[E0425]: cannot find value `TESTS_BINARY` in this scope
    --> tests/by-util/test_dd.rs:1599:43
     |
1599 |     let mut reader_command = Command::new(TESTS_BINARY);
     |                                           ^^^^^^^^^^^^ not found in this scope

This PR fixes the errors by skipping the tests without the "printf" feature.