perf: remove dots from center line in dashboard

Also, recolor the center line as black.

Change-Id: If860801bf7c959ffc8e9600d3d2fb53a88177e78
Reviewed-on: https://go-review.googlesource.com/c/build/+/412377
Reviewed-by: Michael Pratt <mpratt@google.com>
diff --git a/third_party/bandchart/bandchart.js b/third_party/bandchart/bandchart.js
index 5c8bcb0..d9f5450 100644
--- a/third_party/bandchart/bandchart.js
+++ b/third_party/bandchart/bandchart.js
@@ -182,23 +182,10 @@
 
 	svg.append("path")
 		.attr("fill", "none")
-		.attr("stroke", "#375eab")
-		.attr("stroke-width", 3)
+		.attr("stroke", "#212121")
+		.attr("stroke-width", 2.5)
 		.attr("d", line(I))
 
-	// Create dots.
-
-	svg.append("g")
-		.attr("fill", "#375eab")
-		.attr("stroke", "#e0ebf5")
-		.attr("stroke-width", 1)
-		.selectAll("circle")
-		.data(I)
-		.join("circle")
-			.attr("cx", i => xScale(X[i]))
-			.attr("cy", i => yScale(Y[i]))
-			.attr("r", 4);
-
 	// Divide the chart into columns and apply links and hover actions to them.
 	svg.append("g")
 		.attr("stroke", "#2074A0")