Rename Call::Config to CallConfig, keep old name as alias.

We want api/peerconnectioninterface.h (and corresponding build target)
to not depend on call.h, and generally we treat Call as an internal,
non-api, class. But we need CallFactoryInterface in the api in order to
enable use of PeerConnection with or without support for media.

Making CallConfig a top-level class makes it possible to forward declare
it, together with Call, for use in callfactoryinterface.h and
peerconnectioninterface.h.

Delete the peerconnection_and_implicit_call_api target, replaced by
new target callfactory_api, to link between Call and Peerconnection.

Bug: webrtc:7504
Change-Id: I5e3978ef89bcd6705e94536f8676bcf89fc82fe1
Reviewed-on: https://webrtc-review.googlesource.com/46201
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22020}
diff --git a/pc/peerconnectioninternal.h b/pc/peerconnectioninternal.h
index 0f942d2..c276b3d 100644
--- a/pc/peerconnectioninternal.h
+++ b/pc/peerconnectioninternal.h
@@ -18,6 +18,7 @@
 #include <vector>
 
 #include "api/peerconnectioninterface.h"
+#include "call/call.h"
 #include "pc/datachannel.h"
 #include "pc/rtptransceiver.h"