Reduce the size of ResponseHeader and RequestHeader (#1826)

* Reduce sizeof ResponseHeader and RequestHeader

+ Reduce ResponseHeader from 320 to 312 bytes
+ Reduce RequestHeader from 360 to 352 bytes
+ In the benchmark tests, although there is no significant performance improvement, it theoretically reduces memory usage by 2.2% to 2.5%.

* Remove redundant comment

Author: ksw2000