TWCC-PLR -based FecController doesn’t need smoothing; instead, use "null-smoothing", which just returns the last value (if any).
If we end up using TWCC-PLR, we'll just remove smoothing altogether. Until then, this is the least intrusive way to modify the code while still letting it work correctly for RTCP-PLR.
BUG=webrtc:7058
Review-Url: https://codereview.webrtc.org/2687433004
Cr-Commit-Position: refs/heads/master@{#17375}
f0e1f60b0c