Remove internal use of SignalSSLHandshakeError and prepare removal of sigslot dependency from SSLStreamAdapter. Bug: webrtc:11943 Change-Id: I9768e2e31529945620bdd8d0d285042bb2388b7b Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/318881 Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org> Cr-Commit-Position: refs/heads/main@{#40695}