clippy: simplify code according to nightly 'byte_char_slices' lint

https://rust-lang.github.io/rust-clippy/master/index.html#/byte_char_slices

tests/by-util/test_hashsum.rs

@@ -83,7 +83,7 @@ macro_rules! test_digest {
             // The asterisk indicates that the digest was computed in
             // binary mode.
             let n = expected.len();
-            let expected = [&expected[..n - 3], &[b' ', b'-', b'\n']].concat();
+            let expected = [&expected[..n - 3], b" -\n"].concat();
             new_ucmd!()
                 .args(&[DIGEST_ARG, BITS_ARG, "-t"])
                 .pipe_in("a\r\nb\r\nc\r\n")

tests/by-util/test_tr.rs

@@ -1434,8 +1434,8 @@ fn check_complement_set2_too_big() {
 #[test]
 #[cfg(unix)]
 fn test_truncate_non_utf8_set() {
-    let stdin = &[b'\x01', b'a', b'm', b'p', 0xfe_u8, 0xff_u8];
-    let set1 = OsStr::from_bytes(&[b'a', 0xfe_u8, 0xff_u8, b'z']);
+    let stdin = b"\x01amp\xfe\xff";
+    let set1 = OsStr::from_bytes(b"a\xfe\xffz"); // spell-checker:disable-line
     let set2 = OsStr::from_bytes(b"01234");
 
     new_ucmd!()

tests/common/util.rs

@@ -59,7 +59,7 @@ static ALREADY_RUN: &str = " you have already run this UCommand, if you want to
 static MULTIPLE_STDIN_MEANINGLESS: &str = "Ucommand is designed around a typical use case of: provide args and input stream -> spawn process -> block until completion -> return output streams. For verifying that a particular section of the input stream is what causes a particular behavior, use the Command type directly.";
 
 static NO_STDIN_MEANINGLESS: &str = "Setting this flag has no effect if there is no stdin";
-static END_OF_TRANSMISSION_SEQUENCE: &[u8] = &[b'\n', 0x04];
+static END_OF_TRANSMISSION_SEQUENCE: &[u8] = b"\n\x04";
 
 pub const TESTS_BINARY: &str = env!("CARGO_BIN_EXE_coreutils");
 pub const PATH: &str = env!("PATH");
@@ -3081,7 +3081,7 @@ mod tests {
         let result = TestScenario::new("echo").ucmd().arg("Hello world").run();
 
         result.stdout_str_check(|stdout| stdout.ends_with("world\n"));
-        result.stdout_check(|stdout| stdout.get(0..2).unwrap().eq(&[b'H', b'e']));
+        result.stdout_check(|stdout| stdout.get(0..2).unwrap().eq(b"He"));
         result.no_stderr();
     }
 
@@ -3096,7 +3096,7 @@ mod tests {
         ));
 
         result.stderr_str_check(|stderr| stderr.ends_with("world\n"));
-        result.stderr_check(|stderr| stderr.get(0..2).unwrap().eq(&[b'H', b'e']));
+        result.stderr_check(|stdout| stdout.get(0..2).unwrap().eq(b"He"));
         result.no_stdout();
     }