Revert "Add SSLConfig object to IceServer."

This reverts commit 7f1ffcccce563a086da037334aec2d4faa723edb.

Reason for revert: Speculative revert

Original change's description:
> Add SSLConfig object to IceServer.
> 
> This is being added to allow greater configurability to TLS connections.
> tlsAlpnProtocols, tlsEllipticCurves and tlsCertPolicy will be removed from IceServer in a
> follow-up CL.
> 
> Bug: webrtc:9662
> Change-Id: I33cb804b02c26c662ed2a28c76f9a9dc2df40f36
> Reviewed-on: https://webrtc-review.googlesource.com/96020
> Commit-Queue: Diogo Real <diogor@google.com>
> Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
> Reviewed-by: Benjamin Wright <benwright@webrtc.org>
> Reviewed-by: Steve Anton <steveanton@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#24559}

TBR=steveanton@webrtc.org,sakal@webrtc.org,kthelgason@webrtc.org,juberti@webrtc.org,emadomara@webrtc.org,qingsi@webrtc.org,benwright@webrtc.org,diogor@google.com

Change-Id: Iae9fc68b77f743876bda36fc2a04f6d791aae8e2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9662
Reviewed-on: https://webrtc-review.googlesource.com/98000
Reviewed-by: Ying Wang <yinwa@webrtc.org>
Commit-Queue: Ying Wang <yinwa@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24563}

p2p/base/port_unittest.cc

@@ -537,7 +537,8 @@ class PortTest : public testing::Test, public sigslot::has_slots<> {
     return TurnPort::Create(
         &main_, socket_factory, MakeNetwork(addr), 0, 0, username_, password_,
         ProtocolAddress(server_addr, int_proto), kRelayCredentials, 0,
-        std::string(), nullptr, rtc::SSLConfig(), nullptr);
+        std::string(), std::vector<std::string>(), std::vector<std::string>(),
+        nullptr, nullptr);
   }
   RelayPort* CreateGturnPort(const SocketAddress& addr,
                              ProtocolType int_proto,