[NTP::Cleanup] Remove obsolete prefs cleaning and feature definition.

Remove

1) In remote_suggestions_scheduler_impl.cc prefs cleaning procedures
for M59.

2) In features.h an obsolete feature definition, which I missed when
removed the feature itself.

Bug: 
Change-Id: I7bdb6cf0c64db96f0a76eed49fe49cd11df00cdc
Reviewed-on: https://chromium-review.googlesource.com/663180Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Commit-Queue: vitaliii <vitaliii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501259}

components/ntp_snippets/features.h

@@ -46,10 +46,10 @@ extern const base::Feature kCategoryRanker;
 // Feature to allow the new Google favicon server for fetching publisher icons.
 extern const base::Feature kPublisherFaviconsFromNewServerFeature;
 
-// Feature for simple experimental comparision and validation of changes since
+// Feature for simple experimental comparison and validation of changes since
 // M58: enabling this brings back the M58 Stable fetching schedule (which is
 // suitable for Holdback groups).
-// TODO(jkrcal): Remove when the comparision is done (probably after M62).
+// TODO(jkrcal): Remove when the comparison is done (probably after M62).
 extern const base::Feature kRemoteSuggestionsEmulateM58FetchingSchedule;
 
 // Parameter and its values for the kCategoryRanker feature flag.
@@ -123,11 +123,6 @@ constexpr int kNotificationsIgnoredDefaultLimit = 3;
 // have been fetched.
 extern const base::Feature kKeepPrefetchedContentSuggestions;
 
-// Whether remote categories (except articles) which are not present in the last
-// fetch response should be deleted. This feature implicitly depends on
-// kArticleSuggestionsFeature.
-extern const base::Feature kDeleteRemoteCategoriesNotPresentInLastFetch;
-
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_FEATURES_H_

components/ntp_snippets/remote/remote_suggestions_scheduler_impl.cc

@@ -70,7 +70,7 @@ const double kDefaultFetchingIntervalHoursActiveNtpUser[] = {96.0, 48.0, 24.0,
 const double kDefaultFetchingIntervalHoursActiveSuggestionsConsumer[] = {
     48.0, 24.0, 12.0, 12.0, 1.0, 1.0};
 
-// For a simple comparision: fetching intervals that emulate the state really
+// For a simple comparison: fetching intervals that emulate the state really
 // rolled out to 100% M58 Stable. Used for evaluation of later changes. DBL_MAX
 // values simulate this interval being disabled.
 // TODO(jkrcal): Remove when not needed any more, incl. the feature. Probably
@@ -140,11 +140,6 @@ const char* const kTriggerTypesParamValueForEmptyList = "-";
 
 const int kBlockBackgroundFetchesMinutesAfterClearingHistory = 30;
 
-const char kSnippetSoftFetchingIntervalOnUsageEventDeprecated[] =
-    "ntp_snippets.soft_fetching_interval_on_usage_event";
-const char kSnippetSoftFetchingIntervalOnNtpOpenedDeprecated[] =
-    "ntp_snippets.soft_fetching_interval_on_ntp_opened";
-
 // Returns the time interval to use for scheduling remote suggestion fetches for
 // the given interval and user_class.
 base::TimeDelta GetDesiredFetchingInterval(
@@ -461,10 +456,6 @@ RemoteSuggestionsSchedulerImpl::RemoteSuggestionsSchedulerImpl(
   DCHECK(user_classifier);
   DCHECK(profile_prefs);
 
-  // Cleanup procedure in M59. Remove for M62.
-  profile_prefs_->ClearPref(kSnippetSoftFetchingIntervalOnUsageEventDeprecated);
-  profile_prefs_->ClearPref(kSnippetSoftFetchingIntervalOnNtpOpenedDeprecated);
-
   LoadLastFetchingSchedule();
 }
 
@@ -482,12 +473,6 @@ void RemoteSuggestionsSchedulerImpl::RegisterProfilePrefs(
   registry->RegisterInt64Pref(prefs::kSnippetShownFetchingIntervalWifi, 0);
   registry->RegisterInt64Pref(prefs::kSnippetShownFetchingIntervalFallback, 0);
   registry->RegisterInt64Pref(prefs::kSnippetLastFetchAttempt, 0);
-
-  // Cleanup procedure in M59. Remove for M62.
-  registry->RegisterInt64Pref(
-      kSnippetSoftFetchingIntervalOnUsageEventDeprecated, 0);
-  registry->RegisterInt64Pref(kSnippetSoftFetchingIntervalOnNtpOpenedDeprecated,
-                              0);
 }
 
 void RemoteSuggestionsSchedulerImpl::SetProvider(