Delete final remnants of the buzz namespace.

The code using this namespace was deleted in cl
https://codereview.webrtc.org/2617443003.

TBR=pthatcher@webrtc.org
BUG=webrtc:5539

Review-Url: https://codereview.webrtc.org/2622543003
Cr-Commit-Position: refs/heads/master@{#15965}

webrtc/build/sanitizers/lsan_suppressions_webrtc.cc

@@ -58,8 +58,6 @@ char kLSanDefaultSuppressions[] =
 // https://code.google.com/p/webrtc/issues/detail?id=4149 for details.
 "leak:StartDNSLookup\n"
 // https://code.google.com/p/webrtc/issues/detail?id=2527
-"leak:buzz::FakeXmppClient::SendStanza\n"
-"leak:buzz::XmppTask::XmppTask\n"
 "leak:HangoutPubSubClientTest::HangoutPubSubClientTest\n"
 "leak:MucRoomConfigTaskTest::SetUp\n"
 "leak:MucRoomDiscoveryTaskTest::SetUp\n"

webrtc/p2p/base/transportchannelimpl.h

@@ -16,8 +16,6 @@
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/p2p/base/transportchannel.h"
 
-namespace buzz { class XmlElement; }
-
 namespace webrtc {
 class MetricsObserverInterface;
 }