Make RtpData and RtpFeedback destructors public.
Make RtpData and RtpFeedback destructors public.

R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2399004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e5021fe5905e3cad792738e6aaadc6ddc742d42b

sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc