[ios] Remove obsolete TODO from CollectFinalHistograms

After crrev.com/c/953723 the code on iOS and non-iOS platforms has
diverged and there is no code that can be shared.

Bug: None
Change-Id: Ib80dcda88904df5a0d50a392d5d0c3dbbac60c64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2385888
Auto-Submit: Eugene But <eugenebut@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803423}

ios/chrome/browser/metrics/ios_chrome_metrics_service_client.mm

@@ -327,10 +327,6 @@ void IOSChromeMetricsServiceClient::RegisterUKMProviders() {
 void IOSChromeMetricsServiceClient::CollectFinalHistograms() {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  // TODO(ios): Try to extract the flow below into a utility function that is
-  // shared between the iOS port's usage and
-  // ChromeMetricsServiceClient::CollectFinalHistograms()'s usage of
-  // MetricsMemoryDetails.
   task_vm_info task_info_data;
   mach_msg_type_number_t count = sizeof(task_vm_info) / sizeof(natural_t);
   kern_return_t kr =