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}
diff --git a/webrtc/base/objc/RTCMacros.h b/webrtc/base/objc/RTCMacros.h
index 71fa096..4979a2b 100644
--- a/webrtc/base/objc/RTCMacros.h
+++ b/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_