remove _opt suffix from TimeZone::timestamp_micros and use

NaiveDateTime::from_timestamp_micros instead of implementing the same
logic again.

src/offset/mod.rs

@@ -438,15 +438,13 @@ pub trait TimeZone: Sized + Clone {
     /// ```
     /// use chrono::{Utc, TimeZone};
     ///
-    /// assert_eq!(Utc.timestamp_micros_opt(1431648000000).unwrap().timestamp(), 1431648);
+    /// assert_eq!(Utc.timestamp_micros(1431648000000).unwrap().timestamp(), 1431648);
     /// ```
-    fn timestamp_micros_opt(&self, micros: i64) -> LocalResult<DateTime<Self>> {
-        let (mut secs, mut micros) = (micros / 1_000_000, micros % 1_000_000);
-        if micros < 0 {
-            secs -= 1;
-            micros += 1_000_000;
+    fn timestamp_micros(&self, micros: i64) -> LocalResult<DateTime<Self>> {
+        match NaiveDateTime::from_timestamp_micros(micros) {
+            Some(dt) => LocalResult::Single(self.from_utc_datetime(&dt)),
+            None => LocalResult::None,
         }
-        self.timestamp_opt(secs, (micros * 1000) as u32)
     }
 
     /// Parses a string with the specified format string and returns a
@@ -577,20 +575,15 @@ mod tests {
 
     #[test]
     fn test_negative_micros() {
-        let dt = Utc.timestamp_micros_opt(-1_000_000).unwrap();
+        let dt = Utc.timestamp_micros(-1_000_000).unwrap();
         assert_eq!(dt.to_string(), "1969-12-31 23:59:59 UTC");
-        let dt = Utc.timestamp_micros_opt(-999_999).unwrap();
+        let dt = Utc.timestamp_micros(-999_999).unwrap();
         assert_eq!(dt.to_string(), "1969-12-31 23:59:59.000001 UTC");
-        let dt = Utc.timestamp_micros_opt(-1).unwrap();
+        let dt = Utc.timestamp_micros(-1).unwrap();
         assert_eq!(dt.to_string(), "1969-12-31 23:59:59.999999 UTC");
-        let dt = Utc.timestamp_micros_opt(-60_000_000).unwrap();
+        let dt = Utc.timestamp_micros(-60_000_000).unwrap();
         assert_eq!(dt.to_string(), "1969-12-31 23:59:00 UTC");
-        let dt = Utc.timestamp_micros_opt(-3_600_000_000).unwrap();
+        let dt = Utc.timestamp_micros(-3_600_000_000).unwrap();
         assert_eq!(dt.to_string(), "1969-12-31 23:00:00 UTC");
     }
-
-    #[test]
-    fn test_micros_example() {
-        assert_eq!(Utc.timestamp_micros_opt(1431648000000).unwrap().timestamp(), 1431648);
-    }
 }