Move SSLIdentity Generate() implementations from .h to .cc file.

This amends https://codereview.webrtc.org/1683193003/

BUG=
R=hbos@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1701953002 .

Cr-Original-Commit-Position: refs/heads/master@{#11632}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a3dc79e0721f1e3d115ba9b52bb91cb8375d582c
2 files changed