bench: test fetch instead of pull

`pull` is literally `fetch` + `checkout` and our main interest there is downloading, so let's just test fetch instead.

dvc/testing/benchmarks/cli/commands/test_fetch.py

@@ -0,0 +1,3 @@
+def test_fetch(bench_dvc, tmp_dir, dvc, make_dataset, remote):
+    make_dataset(cache=False, dvcfile=True, files=False, remote=True)
+    bench_dvc("fetch")

dvc/testing/benchmarks/cli/commands/test_pull.py

@@ -1,3 +0,0 @@
-def test_pull(bench_dvc, tmp_dir, dvc, make_dataset, remote):
-    make_dataset(cache=False, dvcfile=True, files=False, remote=True)
-    bench_dvc("pull")