Removes storage_driver option from /etc/docker/daemon.json

This setting is applied by minikube in both /etc/docker/daemon.json
and as an override to the service file in
/etc/systemd/system/docker.service.d/10-machine.conf, during
provision phase.

If two such directives are set, docker.service will not start

pkg/minikube/cruntime/docker.go

@@ -541,8 +541,7 @@ func (r *Docker) setCGroup(driver string) error {
 "log-driver": "json-file",
 "log-opts": {
 	"max-size": "100m"
-},
-"storage-driver": "overlay2"
+}
 }
 `, driver)
 	ma := assets.NewMemoryAsset([]byte(daemonConfig), "/etc/docker", "daemon.json", "0644")