Revert "Add sweep_line_region_granularity Finch param."

This reverts commit de838847.

Reason for revert: Given current Finch data (go/janktrackingsweepline),
we have decided to launch JankTrackingSweepLine without running the
previously proposed granularity experiment.

Original change's description:
> Add sweep_line_region_granularity Finch param.
> 
> This controls the degree of region granularity snapping that occurs in
> JankTracker when the sweep line algorithm (JankTrackingSweepLine) is
> enabled.  Previously, the sweep line feature disabled all granularity
> snapping.
> 
> The default param setting, kHigh, matches the degree of granularity
> snapping that is performed without the sweep line algorithm.
> 
> Bug: 581518
> Change-Id: I75a5264b9625349572e6a7f8a7249852e2a8304a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1655984
> Commit-Queue: Steve Kobes <skobes@chromium.org>
> Reviewed-by: Timothy Dresser <tdresser@chromium.org>
> Reviewed-by: Emily Hanley <eyaich@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#668556}

TBR=skobes@chromium.org,tdresser@chromium.org,eyaich@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 581518
Change-Id: Iba95a93d2bc5f0e15495db3e647b0090ef85c680
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1661474Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669665}

third_party/blink/renderer/core/layout/jank_tracker.cc

@@ -4,10 +4,8 @@
 
 #include "third_party/blink/renderer/core/layout/jank_tracker.h"
 
-#include "base/metrics/field_trial_params.h"
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/picture_layer.h"
-#include "third_party/blink/public/common/features.h"
 #include "third_party/blink/renderer/core/frame/local_dom_window.h"
 #include "third_party/blink/renderer/core/frame/local_frame.h"
 #include "third_party/blink/renderer/core/frame/local_frame_client.h"
@@ -28,11 +26,11 @@
 namespace blink {
 
 static constexpr TimeDelta kTimerDelay = TimeDelta::FromMilliseconds(500);
+static const float kRegionGranularitySteps = 60.0;
+// TODO: Vary by Finch experiment parameter.
+static const float kSweepLineRegionGranularity = 1.0;
 static const float kMovementThreshold = 3.0;  // CSS pixels.
 
-// Level of granularity snapping for impact region (see RegionGranularityScale).
-enum GranularitySnapping { kPixel = 1, kLow = 2, kMedium = 3, kHigh = 4 };
-
 static FloatPoint LogicalStart(const FloatRect& rect,
                                const LayoutObject& object) {
   const ComputedStyle* style = object.Style();
@@ -52,29 +50,11 @@ static float GetMoveDistance(const FloatRect& old_rect,
 }
 
 static float RegionGranularityScale(const IntRect& viewport) {
-  static const base::FeatureParam<int> kSweepLineRegionGranularity{
-      &blink::features::kJankTrackingSweepLine, "sweep_line_region_granularity",
-      kHigh};
-
-  GranularitySnapping snapping_type =
-      RuntimeEnabledFeatures::JankTrackingSweepLineEnabled()
-          ? (GranularitySnapping)kSweepLineRegionGranularity.Get()
-          : kHigh;
-  switch (snapping_type) {
-    case kPixel:
-      // Snap to multiples of 1px.
-      return 1.0;
-    case kLow:
-      // Snap to multiples of 2px.
-      return 1 / 2.0;
-    case kMedium:
-      // Snap to multiples of 5px.
-      return 1 / 5.0;
-    case kHigh:
-      // Snap to multiples of 1/60th of min(viewport width, viewport height).
-      return 60.0 / std::min(viewport.Height(), viewport.Width());
-  }
-  NOTREACHED();
+  if (RuntimeEnabledFeatures::JankTrackingSweepLineEnabled())
+    return kSweepLineRegionGranularity;
+
+  return kRegionGranularitySteps /
+         std::min(viewport.Height(), viewport.Width());
 }
 
 static bool EqualWithinMovementThreshold(const FloatPoint& a,