rm: should match GNU's output if multiple slashes in argument

[jhscheer]

rm fails this test: https://github.com/coreutils/coreutils/blob/master/tests/rm/v-slash.sh
The directory and the file are removed, but the stdout doesn't match GNU's stdout.

If ported to rust:

#[test]
fn test_rm_verbose_slash() {
    let (at, mut ucmd) = at_and_ucmd!();
    let dir = "test_rm_verbose_slash_directory";
    let file_a = &format!("{}/test_rm_verbose_slash_file_a", dir);

    at.mkdir(dir);
    at.touch(file_a);

    ucmd.arg("-r")
        .arg("-f")
        .arg("-v")
        .arg(&format!("{}///", dir))
        .succeeds()
        .stdout_only(format!(
            "removed '{}'\nremoved directory '{}'\n",
            file_a, dir
        ));

    assert!(!at.dir_exists(dir));
    assert!(!at.file_exists(file_a));
}

the output is:

'test_rm::test_rm_verbose_slash' panicked at 'assertion failed: `(left == right)`
  left: `"removed directory \'test_rm_verbose_slash_directory///\'\n"`,
 right: `"removed \'test_rm_verbose_slash_directory/test_rm_verbose_slash_file_a\'\nremoved directory \'test_rm_verbose_slash_directory\'\n"`'

Related #1768

[marvin-bitterlich]

I took a stab at this in #1988 as a first contribution to this project :)