Classes AsyncProxyServerSocket, AsyncSSLServerSocket, and
AsyncSSLServerSocket are used only by test and example code.
Moved to server_socket_adapters.{cc,h}, and to the
rtc_base_tests_utils build target.
In the process, also deleted a few ancient and unattributed TODO
comments.
Bug: webrtc:9798
Change-Id: I21279c92bd8f1354fab7eeaf1f9697fedfc760e1
Reviewed-on: https://webrtc-review.googlesource.com/c/107735
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26039}
