Remove a test of legacy buildpack

tests/unit/test_cache_from.py

@@ -50,23 +50,3 @@ def test_cache_from_docker(tmpdir):
     called_args, called_kwargs = fake_client.build.call_args
     assert "cache_from" in called_kwargs
     assert called_kwargs["cache_from"] == cache_from
-
-
-def test_cache_from_legacy(tmpdir):
-    cache_from = ["image-1:latest"]
-    fake_log_value = {"stream": "fake"}
-    fake_client = MagicMock(spec=docker.APIClient)
-    fake_client.build.return_value = iter([fake_log_value])
-    extra_build_kwargs = {"somekey": "somevalue"}
-
-    # Test legacy docker image
-    with tmpdir.join("Dockerfile").open("w") as f:
-        f.write("FROM andrewosh/binder-base\n")
-
-    for line in LegacyBinderDockerBuildPack().build(
-        fake_client, "image-2", 100, {}, cache_from, extra_build_kwargs
-    ):
-        assert line == fake_log_value
-    called_args, called_kwargs = fake_client.build.call_args
-    assert "cache_from" in called_kwargs
-    assert called_kwargs["cache_from"] == cache_from