docs: remove leading underscores

Author: Lingxuan-Ye

docs/chapter_array_and_linkedlist/list.md

@@ -684,15 +684,15 @@
 
     ```rust title="list.rs"
     // 通过索引遍历列表
-    let mut _count = 0;
+    let mut count = 0;
     for i in 0..nums.len() {
-        _count += nums[i];
+        count += nums[i];
     }
 
     // 直接遍历列表元素
-    _count = 0;
+    count = 0;
     for num in &nums {
-        _count += num;
+        count += num;
     }
     ```
 

docs/chapter_hashing/hash_map.md

@@ -254,11 +254,11 @@
 
     /* 查询操作 */
     // 向哈希表中输入键 key ，得到值 value
-    let _name: Option<&String> = map.get(&15937);
+    let name: Option<&String> = map.get(&15937);
 
     /* 删除操作 */
     // 在哈希表中删除键值对 (key, value)
-    let _removed_value: Option<String> = map.remove(&10583);
+    let removed_value: Option<String> = map.remove(&10583);
     ```
 
 === "C"