Revert "PageLoadMetrics: Add PageLoadTrackerTest"

This reverts commit 61176b7.

Reason for revert: This introduced 2 failing tests on Android.
See: https://crbug.com/1309799

Original change's description:
> PageLoadMetrics: Add PageLoadTrackerTest
>
> Bug: 1301880
> Change-Id: I65fbe30fe3d5266fa4146b0946043d7568256ec3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3546196
> Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
> Reviewed-by: Annie Sullivan <sullivan@chromium.org>
> Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#984629}

Bug: 1301880
Change-Id: I1b9b95cb6e8ba67bacb4bb5e9f0e475edca1907a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3548276
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Owners-Override: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#984739}

components/page_load_metrics/browser/BUILD.gn

@@ -116,7 +116,6 @@ source_set("unit_tests") {
     "observers/use_counter_page_load_metrics_observer_unittest.cc",
     "page_load_metrics_memory_tracker_unittest.cc",
     "page_load_metrics_util_unittest.cc",
-    "page_load_tracker_unittest.cc",
     "resource_tracker_unittest.cc",
     "responsiveness_metrics_normalization_unittest.cc",
   ]

components/page_load_metrics/browser/observers/early_hints_page_load_metrics_observer_unittest.cc

@@ -55,6 +55,7 @@ class EarlyHintsPageLoadMetricsObserverTest
   }
 };
 
+// TODO(https://crbug.com/1301880): Add tests for other PageTypes.
 TEST_F(EarlyHintsPageLoadMetricsObserverTest, PageType) {
   NavigateAndCommit(GURL(kTestUrl));
   PopulateTimingForHistograms();