Fix unnecessary boolean 'not' operation found by clippy pedantic

[sylvestre]

Example:

warning: unnecessary boolean `not` operation
   --> tests/by-util/test_du.rs:306:5
    |
306 | /     if !uucore::os::is_wsl_1() {
307 | |         assert_eq!(s, "8\tsubdir/links/deeper_dir\n24\tsubdir/links\n");
308 | |     } else {
309 | |         assert_eq!(s, "0\tsubdir/links/deeper_dir\n8\tsubdir/links\n");
310 | |     }
    | |_____^
    |
    = help: remove the `!` and swap the blocks of the `if`/`else`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_not_else

Found with:
cargo +nightly clippy --features unix --allow-dirty -- -W clippy::pedantic

[papparapa]

Maybe cargo +nightly clippy --features unix -- -A clippy::pedantic -W clippy::if_not_else is useful to pick up this specific type of warning.

[sylvestre]

Two more occurrences:

warning: unnecessary boolean `not` operation
    --> tests/common/util.rs:2508:5
     |
2508 | /     if !is_ci() {
2509 | |         // check if we can run 'sudo'
2510 | |         log_info("run", "sudo -E --non-interactive whoami");
2511 | |         match Command::new("sudo")
...    |
2539 | |         Err(format!("{UUTILS_INFO}: {}", "cannot run inside CI"))
2540 | |     }
     | |_____^
     |
     = help: remove the `!` and swap the blocks of the `if`/`else`
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_not_else
     = note: `-W clippy::if-not-else` implied by `-W clippy::pedantic`

warning: unnecessary boolean `not` operation
    --> tests/common/util.rs:2993:9
     |
2993 | /         if !is_ci() {
2994 | |             // Skip test if we can't guarantee non-interactive `sudo`, or if we're not "root"
2995 | |             if let Ok(output) = Command::new("sudo")
2996 | |                 .env("LC_ALL", "C")
...    |
3013 | |             println!("TEST SKIPPED (cannot run inside CI)");
3014 | |         }
     | |_________^
     |
     = help: remove the `!` and swap the blocks of the `if`/`else`
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_not_else

[sylvestre]

There is way more :)

   --> src/uucore/src/lib/mods/quoting_style.rs:262:13
    |
262 | /             if !show_control {
263 | |                 name.to_string_lossy()
264 | |                     .chars()
265 | |                     .flat_map(|c| EscapedChar::new_literal(c).hide_control())
...   |
268 | |                 name.to_string_lossy().into_owned()
269 | |             }
    | |_____________^

[cakebaker]

Fixed in #4647