Remove last vestige of APIs that are deprecated in iOS 8.

ios/chrome/browser/crash_report/crash_report_background_uploader.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/crash_report/crash_report_background_uploader.h"
 
 #import <UIKit/UIKit.h>
 
 #include "base/logging.h"
 #include "base/mac/scoped_block.h"
@@ skipping 159 matching lines @@
   static CrashReportBackgroundUploader* instance =
       [[CrashReportBackgroundUploader alloc] init];
   return instance;
 }
 
 + (NSURLSession*)BreakpadBackgroundURLSessionWithCompletionHandler:
         (ProceduralBlock)completionHandler {
   static NSURLSession* session = nil;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
-
-    // TODO(olivierrobin) When all bots compile with iOS8 release SDK, use
-    // only backgroundSessionConfigurationWithIdentifier.
     NSURLSessionConfiguration* sessionConfig = [NSURLSessionConfiguration
-        backgroundSessionConfiguration:kBackgroundReportUploader];
-
+        backgroundSessionConfigurationWithIdentifier:kBackgroundReportUploader];
     session = [NSURLSession
         sessionWithConfiguration:sessionConfig
                         delegate:[UrlSessionDelegate sharedInstance]
                    delegateQueue:[NSOperationQueue mainQueue]];
   });
   DCHECK(session);
   if (completionHandler) {
     [[UrlSessionDelegate sharedInstance]
         setSessionCompletionHandler:completionHandler];
   }
@@ skipping 161 matching lines @@
           integerForKey:kReportsUploadedInBackground];
   return uploadedCrashReportsInBackgroundCount > 0;
 }
 
 + (void)resetReportsUploadedInBackgroundCount {
   [[NSUserDefaults standardUserDefaults]
       removeObjectForKey:kReportsUploadedInBackground];
 }
 
 @end