Also delete the base class MemoryStreamBase.
Bug: webrtc:6424
Change-Id: I7eec40ecff17c7c65fdf55882bccb2abaf1d5d84
Reviewed-on: https://webrtc-review.googlesource.com/c/108622
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25494}