Improve the jerry port api documents. (#4977)

Notable changes:
  - Remove the comments in port impl, that's easily getting to in-consistence
  - Sync the jerryscript-port.h and 05.PORT-API.md
  - Fixes the invalid comment in port codes

JerryScript-DCO-1.0-Signed-off-by: Yonggang Luo luoyonggang@gmail.com

jerry-port/win/jerry-port-win-date.c

@@ -72,12 +72,6 @@ filetime_to_unix_time (LPFILETIME ft_p)
   return (double) (((LONGLONG) date.QuadPart - UNIX_EPOCH_IN_TICKS) / TICKS_PER_MS);
 } /* filetime_to_unix_time */
 
-/**
- * Default implementation of jerry_port_local_tza.
- *
- * @return offset between UTC and local time at the given unix timestamp, if
- *         available. Otherwise, returns 0, assuming UTC time.
- */
 int32_t
 jerry_port_local_tza (double unix_ms)
 {
@@ -115,11 +109,6 @@ jerry_port_local_tza (double unix_ms)
   return 0;
 } /* jerry_port_local_tza */
 
-/**
- * Default implementation of jerry_port_current_time.
- *
- * @return milliseconds since Unix epoch
- */
 double
 jerry_port_current_time (void)
 {