Revert of Adding error output param to SetConfiguration, using new RTCError type. (patchset #4 id:60001 of https://codereview.webrtc.org/2587133004/ )

Reason for revert:
Broke chromium FYI bot because the chromium mock PC overrides the method whose signature is changing.

Also broke a downstream internal test, which I need to investigate further.

Original issue's description:
> Adding error output param to SetConfiguration, using new RTCError type.
>
> Most notably, will return "INVALID_MODIFICATION" if a field in the
> configuration was modified and modification of that field isn't supported.
>
> Also changing RTCError to a class that wraps an enum type, because it will
> eventually need to hold other information (like SDP line number), to match
> the RTCError that was recently added to the spec:
> https://github.com/w3c/webrtc-pc/pull/850
>
> BUG=webrtc:6916
>
> Review-Url: https://codereview.webrtc.org/2587133004
> Cr-Commit-Position: refs/heads/master@{#15777}
> Committed: https://chromium.googlesource.com/external/webrtc/+/7a5fa6cd6173adbe32aedc1aedc872478121f5ed

TBR=pthatcher@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6916

Review-Url: https://codereview.webrtc.org/2600813002
Cr-Commit-Position: refs/heads/master@{#15778}
diff --git a/webrtc/api/peerconnectionproxy.h b/webrtc/api/peerconnectionproxy.h
index bc1cd5e..2110ee2 100644
--- a/webrtc/api/peerconnectionproxy.h
+++ b/webrtc/api/peerconnectionproxy.h
@@ -72,10 +72,9 @@
   PROXY_METHOD2(void, SetRemoteDescription, SetSessionDescriptionObserver*,
                 SessionDescriptionInterface*)
   PROXY_METHOD0(PeerConnectionInterface::RTCConfiguration, GetConfiguration);
-  PROXY_METHOD2(bool,
+  PROXY_METHOD1(bool,
                 SetConfiguration,
-                const PeerConnectionInterface::RTCConfiguration&,
-                RTCError*);
+                const PeerConnectionInterface::RTCConfiguration&);
   PROXY_METHOD1(bool, AddIceCandidate, const IceCandidateInterface*)
   PROXY_METHOD1(bool,
                 RemoveIceCandidates,