[scheduler] Remove unnecessary include of Blink's legacy histogram.h

Blink allows use of the //base histogram helpers, so the goal is to
delete the Blink-specific histogram helpers and standardize on //base.

Bug: 1047547
Change-Id: I6a796dde4437d58b67875edc9b535b761394b509
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053966
Auto-Submit: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740991}

third_party/blink/renderer/platform/scheduler/DEPS

@@ -52,7 +52,6 @@ include_rules = [
   "+services/metrics",
 
   "+third_party/blink/renderer/platform/bindings/parkable_string_manager.h",
-  "+third_party/blink/renderer/platform/instrumentation/histogram.h",
   "+third_party/blink/renderer/platform/instrumentation",
   "+third_party/blink/renderer/platform/platform_export.h",
   "+third_party/blink/renderer/platform/runtime_enabled_features.h",

third_party/blink/renderer/platform/scheduler/worker/worker_thread_scheduler.cc

@@ -21,7 +21,6 @@
 #include "services/metrics/public/cpp/ukm_builders.h"
 #include "third_party/blink/public/common/thread_safe_browser_interface_broker_proxy.h"
 #include "third_party/blink/public/platform/platform.h"
-#include "third_party/blink/renderer/platform/instrumentation/histogram.h"
 #include "third_party/blink/renderer/platform/scheduler/common/features.h"
 #include "third_party/blink/renderer/platform/scheduler/common/process_state.h"
 #include "third_party/blink/renderer/platform/scheduler/common/throttling/task_queue_throttler.h"