IWYU openssl-related files and remove Windows-specific bits

Done by
  find rtc_base/ -name "*ssl*.h" -o -name "*ssl*.cc" | xargs tools_webrtc/iwyu/apply-include-cleaner
followed by
  tools_webrtc/gn_check_autofix.py -C out/Default/
and git cl format.

This has previously been problematic but adding openssl/*.h to
the include cleaner ignore list makes this possible.

Also remove the WEBRTC_WIN specific handling which does not seem to be required at least for BoringSSL.

Bug: webrtc:42226242
Change-Id: I71dc1df56f3fcf95e50971388e53ba60aaa66e59
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/395641
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@meta.com>
Cr-Commit-Position: refs/heads/main@{#44923}