cmd/bench: run the default set of sweet benchmarks, not all of them

We've retired two benchmarks, the biogo benchmarks, from the default
set. Make sure they don't get run as part of the perf builder.

Change-Id: I19f9fa81e7901e8de65b1839f978a965336fef7d
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/615417
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

cmd/bench/sweet.go

@@ -105,7 +105,7 @@ func sweet(tcs []*toolchain) (err error) {
 	workDir := filepath.Join(tmpDir, "work")
 	cmd = exec.Command(
 		sweetBin, "run",
-		"-run", "all",
+		"-run", "default",
 		"-count", "10",
 		"-bench-dir", filepath.Join(sweetRoot, "benchmarks"),
 		"-cache", assetsCacheDir,