docs: update errors.md

Delete duplicate code blocks.

src/advance/errors.md

@@ -93,37 +93,6 @@ fn main() {
 }
 ```
 
-```rust
-fn main() {
-    // and_then with Option
-    let s1 = Some("some1");
-    let s2 = Some("some2");
-    let fn_some = |_| Some("some2"); // 类似于: let fn_some = |_| -> Option<&str> { Some("some2") };
-
-    let n: Option<&str> = None;
-    let fn_none = |_| None;
-
-    assert_eq!(s1.and_then(fn_some), s2); // Some1 and_then Some2 = Some2
-    assert_eq!(s1.and_then(fn_none), n);  // Some and_then None = None
-    assert_eq!(n.and_then(fn_some), n);   // None and_then Some = None
-    assert_eq!(n.and_then(fn_none), n);   // None1 and_then None2 = None1
-
-    // and_then with Result
-    let o1: Result<&str, &str> = Ok("ok1");
-    let o2: Result<&str, &str> = Ok("ok2");
-    let fn_ok = |_| Ok("ok2"); // 类似于: let fn_ok = |_| -> Result<&str, &str> { Ok("ok2") };
-
-    let e1: Result<&str, &str> = Err("error1");
-    let e2: Result<&str, &str> = Err("error2");
-    let fn_err = |_| Err("error2");
-
-    assert_eq!(o1.and_then(fn_ok), o2);  // Ok1 and_then Ok2 = Ok2
-    assert_eq!(o1.and_then(fn_err), e2); // Ok and_then Err = Err
-    assert_eq!(e1.and_then(fn_ok), e1);  // Err and_then Ok = Err
-    assert_eq!(e1.and_then(fn_err), e1); // Err1 and_then Err2 = Err1
-}
-```
-
 #### filter
 
 `filter` 用于对 `Option` 进行过滤：