chmod: replace walkdir with std::fs

walkdir filters some files that need to be modified, for example, files inside an unreadable folder.

Cargo.lock

@@ -2385,7 +2385,6 @@ dependencies = [
  "clap 3.0.10",
  "libc",
  "uucore",
- "walkdir",
 ]
 
 [[package]]

src/uu/chmod/Cargo.toml

@@ -18,7 +18,6 @@ path = "src/chmod.rs"
 clap = { version = "3.0", features = ["wrap_help", "cargo"] }
 libc = "0.2.42"
 uucore = { version=">=0.0.11", package="uucore", path="../../uucore", features=["fs", "mode"] }
-walkdir = "2.2"
 
 [[bin]]
 name = "chmod"

src/uu/chmod/src/chmod.rs

@@ -18,7 +18,6 @@ use uucore::libc::mode_t;
 #[cfg(not(windows))]
 use uucore::mode;
 use uucore::{format_usage, show_error, InvalidEncodingHandling};
-use walkdir::WalkDir;
 
 static ABOUT: &str = "Change the mode of each FILE to MODE.
  With --reference, change the mode of each FILE to that of RFILE.";
@@ -227,10 +226,17 @@ impl Chmoder {
             if !self.recursive {
                 r = self.chmod_file(file).and(r);
             } else {
-                for entry in WalkDir::new(&filename).into_iter().filter_map(|e| e.ok()) {
-                    let file = entry.path();
-                    r = self.chmod_file(file).and(r);
-                }
+                r = self.walk_dir(file);
+            }
+        }
+        r
+    }
+
+    fn walk_dir(&self, file_path: &Path) -> UResult<()> {
+        let mut r = self.chmod_file(file_path);
+        if file_path.is_dir() {
+            for dir_entry in fs::read_dir(file_path)? {
+                r = self.walk_dir(dir_entry?.path().as_path());
             }
         }
         r