Delete unused classes from stream.cc

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2754033003
Cr-Original-Commit-Position: refs/heads/master@{#17281}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e9ad37ca068ba5cf2bafe52692e548f7632c3c6c
2 files changed