Cleanup noise provider stragglers in AdsPLMO unittests

There are a few tests in AdsPLMO that still create a mock noise
provider with 0 noise, even though this is now the default for all
tests after https://crrev.com/c/1849130 .These tests landed shortly
after that change.

Change-Id: Icd8a1468b38a2943dcf94f148249a5e6f0ba96c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869471Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: John Delaney <johnidel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708191}

chrome/browser/page_load_metrics/observers/ad_metrics/ads_page_load_metrics_observer_unittest.cc

@@ -2022,9 +2022,6 @@ TEST_F(AdsPageLoadMetricsObserverTest,
   feature_list.InitAndEnableFeature(features::kHeavyAdIntervention);
 
   RenderFrameHost* main_frame = NavigateMainFrame(kNonAdUrl);
-
-  OverrideHeavyAdNoiseProvider(
-      std::make_unique<MockNoiseProvider>(0 /* network noise */));
   RenderFrameHost* ad_frame = CreateAndNavigateSubFrame(kAdUrl, main_frame);
 
   // Add enough data to trigger the intervention.
@@ -2043,9 +2040,6 @@ TEST_F(AdsPageLoadMetricsObserverTest,
   feature_list.InitAndDisableFeature(features::kHeavyAdIntervention);
 
   RenderFrameHost* main_frame = NavigateMainFrame(kNonAdUrl);
-
-  OverrideHeavyAdNoiseProvider(
-      std::make_unique<MockNoiseProvider>(0 /* network noise */));
   RenderFrameHost* ad_frame = CreateAndNavigateSubFrame(kAdUrl, main_frame);
 
   // Add enough data to trigger the intervention.
@@ -2067,9 +2061,6 @@ TEST_F(AdsPageLoadMetricsObserverTest, HeavyAdPageReload_MetricsRecorded) {
   feature_list.InitAndEnableFeature(features::kHeavyAdIntervention);
 
   RenderFrameHost* main_frame = NavigateMainFrame(kNonAdUrl);
-
-  OverrideHeavyAdNoiseProvider(
-      std::make_unique<MockNoiseProvider>(0 /* network noise */));
   RenderFrameHost* ad_frame = CreateAndNavigateSubFrame(kAdUrl, main_frame);
 
   // Add enough data to trigger the intervention.
@@ -2094,9 +2085,6 @@ TEST_F(AdsPageLoadMetricsObserverTest,
   feature_list.InitAndEnableFeature(features::kHeavyAdIntervention);
 
   RenderFrameHost* main_frame = NavigateMainFrame(kNonAdUrl);
-
-  OverrideHeavyAdNoiseProvider(
-      std::make_unique<MockNoiseProvider>(0 /* network noise */));
   RenderFrameHost* ad_frame = CreateAndNavigateSubFrame(kAdUrl, main_frame);
 
   // Don't load enough to reach the heavy ad threshold.