Update readmes with new cli install (#12847)

Old command still works. Just simplifying.

Merge after releasing CLI 0.0.15

libs/cli/langchain_cli/package_template/README.md

@@ -11,7 +11,7 @@ TODO: What environment variables need to be set (if any)
 To use this package, you should first have the LangChain CLI installed:
 
 ```shell
-pip install -U "langchain-cli[serve]"
+pip install -U langchain-cli
 ```
 
 To create a new LangChain project and install this as the only package, you can do:

libs/cli/langchain_cli/project_template/README.md

@@ -5,7 +5,7 @@
 Install the LangChain CLI if you haven't yet
 
 ```bash
-pip install -U "langchain-cli[serve]"
+pip install -U langchain-cli
 ```
 
 ## Adding packages