We no longer use compilers that can't =default move construction and assignment

Review URL: https://codereview.webrtc.org/1891483006

Cr-Original-Commit-Position: refs/heads/master@{#12376}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6ca0a31708ed1ddb06c060ceed5c5d5170af485c
3 files changed