Revert "Raise exception when log into Facebook using OAuth. (#3138)" (#3208) (#3209)

This reverts commit 393d060.

Author: ryanwilson

Firebase/Auth/Source/AuthProvider/OAuth/FIROAuthProvider.m

@@ -23,11 +23,9 @@
 #import "FIRAuthBackend.h"
 #import "FIRAuth_Internal.h"
 #import "FIRAuthErrorUtils.h"
-#import "FIRAuthExceptionUtils.h"
 #import "FIRAuthGlobalWorkQueue.h"
 #import "FIRAuthRequestConfiguration.h"
 #import "FIRAuthWebUtils.h"
-#import "FIRFacebookAuthProvider.h"
 #import "FIROAuthCredential_Internal.h"
 #import "FIROAuthCredential.h"
 
@@ -167,12 +165,6 @@ - (void)getCredentialWithUIDelegate:(nullable id<FIRAuthUIDelegate>)UIDelegate
     @return An Instance of @c FIROAuthProvider.
   */
 - (nullable instancetype)initWithProviderID:(NSString *)providerID auth:(FIRAuth *)auth {
-  if ([providerID isEqual:FIRFacebookAuthProviderID]) {
-    [FIRAuthExceptionUtils raiseInvalidParameterExceptionWithReason:
-        @"Sign in with Facebook is not supported via this method; the Facebook TOS "
-         "dictate that you must use the Facebook iOS SDK for Facebook login."];
-    return nil;
-  }
   self = [super init];
   if (self) {
     _auth = auth;