docs: fix PGVector import examples (#123)

Co-authored-by: Eugene Yurtsev <[email protected]>

Author: JonZeolla

examples/vectorstore.ipynb

@@ -68,7 +68,6 @@
    "outputs": [],
    "source": [
     "from langchain_cohere import CohereEmbeddings\n",
-    "from langchain_postgres import PGVector\n",
     "from langchain_postgres.vectorstores import PGVector\n",
     "from langchain_core.documents import Document\n",
     "\n",

langchain_postgres/vectorstores.py

@@ -269,7 +269,6 @@ class PGVector(VectorStore):
     Instantiate:
         .. code-block:: python
 
-            from langchain_postgres import PGVector
             from langchain_postgres.vectorstores import PGVector
             from langchain_openai import OpenAIEmbeddings