fix: drop swarmkit/etcd dep

Part of coop-cloud/go-abra#57.

client/stack/options.go

@@ -0,0 +1,15 @@
+package stack
+
+// Deploy holds docker stack deploy options
+type Deploy struct {
+	Composefiles     []string
+	Namespace        string
+	ResolveImage     string
+	SendRegistryAuth bool
+	Prune            bool
+}
+
+// Remove holds docker stack remove options
+type Remove struct {
+	Namespaces []string
+}