Revert "Add ios bindings for PeerConnectionState."

This reverts commit 586725dc9a508c7d3e82b5a625a5ee7e8b1a4e17.

Reason for revert: misses a check to see if the optional callback is implemented.

Original change's description:
> Add ios bindings for PeerConnectionState.
> 
> This change makes it possible for ios apps to use the new standards-compliant PeerConnectionState.
> 
> Bug: webrtc:9977
> Change-Id: Icf69bb1faa0383ae239cb7508f2a740a2d489697
> Reviewed-on: https://webrtc-review.googlesource.com/c/110502
> Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#25651}

TBR=kthelgason@webrtc.org,jonasolsson@webrtc.org

Change-Id: Iff919e9876e6b8dddc6d8ab7df302081d0cfa917
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9977
Reviewed-on: https://webrtc-review.googlesource.com/c/111062
Reviewed-by: Jonas Olsson <jonasolsson@webrtc.org>
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25659}
diff --git a/sdk/objc/api/peerconnection/RTCPeerConnection.h b/sdk/objc/api/peerconnection/RTCPeerConnection.h
index 393a50b..0179ec0 100644
--- a/sdk/objc/api/peerconnection/RTCPeerConnection.h
+++ b/sdk/objc/api/peerconnection/RTCPeerConnection.h
@@ -57,16 +57,6 @@
   RTCIceConnectionStateCount,
 };
 
-/** Represents the combined ice+dtls connection state of the peer connection. */
-typedef NS_ENUM(NSInteger, RTCPeerConnectionState) {
-  RTCPeerConnectionStateNew,
-  RTCPeerConnectionStateConnecting,
-  RTCPeerConnectionStateConnected,
-  RTCPeerConnectionStateDisconnected,
-  RTCPeerConnectionStateFailed,
-  RTCPeerConnectionStateClosed,
-};
-
 /** Represents the ice gathering state of the peer connection. */
 typedef NS_ENUM(NSInteger, RTCIceGatheringState) {
   RTCIceGatheringStateNew,
@@ -125,14 +115,11 @@
  *  This is only called with RTCSdpSemanticsUnifiedPlan specified.
  */
 @optional
-/** Called any time the PeerConnectionState changes. */
-- (void)peerConnection:(RTCPeerConnection *)peerConnection
-    didChangeConnectionState:(RTCPeerConnectionState)newState;
-
 - (void)peerConnection:(RTCPeerConnection *)peerConnection
     didStartReceivingOnTransceiver:(RTCRtpTransceiver *)transceiver;
 
 /** Called when a receiver and its track are created. */
+@optional
 - (void)peerConnection:(RTCPeerConnection *)peerConnection
         didAddReceiver:(RTCRtpReceiver *)rtpReceiver
                streams:(NSArray<RTCMediaStream *> *)mediaStreams;
@@ -158,7 +145,6 @@
 @property(nonatomic, readonly, nullable) RTCSessionDescription *remoteDescription;
 @property(nonatomic, readonly) RTCSignalingState signalingState;
 @property(nonatomic, readonly) RTCIceConnectionState iceConnectionState;
-@property(nonatomic, readonly) RTCPeerConnectionState connectionState;
 @property(nonatomic, readonly) RTCIceGatheringState iceGatheringState;
 @property(nonatomic, readonly, copy) RTCConfiguration *configuration;