Delete Value::as_i128

This is adequately supported by `value.as_number().and_then(Number::as_i128)`

src/value/mod.rs

@@ -635,24 +635,6 @@ impl Value {
         }
     }
 
-    /// If the `Value` is an integer, represent it as i128 if possible. Returns
-    /// None otherwise.
-    ///
-    /// ```
-    /// # use serde_json::json;
-    /// #
-    /// let v = json!({ "a": 64, "b": 256.0 });
-    ///
-    /// assert_eq!(v["a"].as_i128(), Some(64));
-    /// assert_eq!(v["b"].as_i128(), None);
-    /// ```
-    pub fn as_i128(&self) -> Option<i128> {
-        match self {
-            Value::Number(n) => n.as_i128(),
-            _ => None,
-        }
-    }
-
     /// If the `Value` is an integer, represent it as u64 if possible. Returns
     /// None otherwise.
     ///