Fix imports for deleting compute cluster (#3158)

* add cells to delete compute clusters

* remove extraneous import

sdk/python/resources/compute/compute.ipynb

@@ -329,7 +329,7 @@
    },
    "outputs": [],
    "source": [
-    "from azure.ai.ml.entities import ComputeInstance, AmlCompute\n",
+    "from azure.ai.ml.entities import AmlCompute\n",
     "\n",
     "ml_client.compute.begin_delete(cluster_basic.name).wait()"
    ]
@@ -340,7 +340,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from azure.ai.ml.entities import ComputeInstance, AmlCompute\n",
+    "from azure.ai.ml.entities import AmlCompute\n",
     "\n",
     "ml_client.compute.begin_delete(cluster_low_pri.name).wait()"
    ]