`LastReceivedNTP()` does not need to be part of the public members of `ModuleRtpRtcpImpl` and `ModuleRtpRtcpImpl2` since it is used only once in the same class. This change is requried by the child CL [1] which adds a public getter needed to add remote-outbound stats. [1] https://webrtc-review.googlesource.com/c/src/+/211041 Bug: webrtc:12529 Change-Id: I82cfea5ee795de37fffa3d759ce9f581ca775d55 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/211043 Commit-Queue: Alessio Bazzica <alessiob@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33420}