deps: remove langchain

Remove langchain and the associated pipeline to simplify our codebase
and reduce our exposure to problem coming from third party dependencies.

Author: goneri

ansible_ai_connect/ai/api/model_pipelines/__init__.py

@@ -2,7 +2,6 @@
 import ansible_ai_connect.ai.api.model_pipelines.dummy.pipelines  # noqa
 import ansible_ai_connect.ai.api.model_pipelines.http.configuration  # noqa
 import ansible_ai_connect.ai.api.model_pipelines.http.pipelines  # noqa
-import ansible_ai_connect.ai.api.model_pipelines.langchain.pipelines  # noqa
 import ansible_ai_connect.ai.api.model_pipelines.llamacpp.configuration  # noqa
 import ansible_ai_connect.ai.api.model_pipelines.llamacpp.pipelines  # noqa
 import ansible_ai_connect.ai.api.model_pipelines.llamastack.configuration  # noqa