perf: update the default benchmarks' suffixes from -8 to -16

We moved from 8 core machines for performance tests recently to 16
core machines. Some of the benchmark names changed as a result. This
change updates those benchmarks that appear on the landing page.

Change-Id: If8964aff3491da3a5dd7d75d1ea7a9ab12365e88
Reviewed-on: https://go-review.googlesource.com/c/build/+/570239
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

perf/app/dashboard.go

@@ -222,15 +222,15 @@ func fetchDefaultBenchmarks(ctx context.Context, qc api.QueryAPI, start, end tim
 			unit: "sec/op",
 		},
 		{
-			name: "RegexMatch-8",
+			name: "RegexMatch-16",
 			unit: "sec/op",
 		},
 		{
-			name: "BuildJSON-8",
+			name: "BuildJSON-16",
 			unit: "sec/op",
 		},
 		{
-			name: "ZapJSON-8",
+			name: "ZapJSON-16",
 			unit: "sec/op",
 		},
 	}