Remove WEBRTC_IOS from RTCPeerConnectionFactory public header.

We shouldn't make external users define this flag to use our file.

BUG=

Review URL: https://codereview.webrtc.org/1825713003

Cr-Commit-Position: refs/heads/master@{#12106}

webrtc/api/objc/RTCPeerConnectionFactory.h

@@ -12,9 +12,7 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
-#if defined(WEBRTC_IOS)
 @class RTCAVFoundationVideoSource;
-#endif
 @class RTCAudioTrack;
 @class RTCConfiguration;
 @class RTCMediaConstraints;
@@ -28,11 +26,9 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)init NS_DESIGNATED_INITIALIZER;
 
-#if defined(WEBRTC_IOS)
 /** Initialize an RTCAVFoundationVideoSource with constraints. */
 - (RTCAVFoundationVideoSource *)avFoundationVideoSourceWithConstraints:
     (nullable RTCMediaConstraints *)constraints;
-#endif
 
 /** Initialize an RTCAudioTrack with an id. */
 - (RTCAudioTrack *)audioTrackWithTrackId:(NSString *)trackId;

webrtc/api/objc/RTCPeerConnectionFactory.mm

@@ -44,13 +44,16 @@
   return self;
 }
 
-#if defined(WEBRTC_IOS)
+
 - (RTCAVFoundationVideoSource *)avFoundationVideoSourceWithConstraints:
     (nullable RTCMediaConstraints *)constraints {
+#if defined(WEBRTC_IOS)
   return [[RTCAVFoundationVideoSource alloc] initWithFactory:self
                                                  constraints:constraints];
-}
+#else
+  return nil;
 #endif
+}
 
 - (RTCAudioTrack *)audioTrackWithTrackId:(NSString *)trackId {
   return [[RTCAudioTrack alloc] initWithFactory:self

webrtc/base/objc/RTCMacros.h

@@ -23,4 +23,4 @@
 #define RTC_FWD_DECL_OBJC_CLASS(classname) typedef struct objc_object classname
 #endif
 
-#endif // WEBRTC_BASE_OBJC_RTC_MACROS_H_
+#endif  // WEBRTC_BASE_OBJC_RTC_MACROS_H_