remove deprecated zilliz cloud pipeline doc (#1264)

## Overview
[Zilliz
Pipeline](https://docs.zilliz.com/reference/restful/create-pipeline) is
a legacy feature that has been offline. While LangChain Milvus
Integration v0.3 is outdated, its docs still include Zilliz Pipeline
introductions—this risks confusing users (e.g., leading them to attempt
using the retired feature). We propose taking this v0.3 documentation
offline to remove obsolete content and avoid user confusion.

## Type of change

**Type:** Remove outdated content

## Related issues/PRs
langchain-ai/langchain#33719

<!-- For LangChain employees, if applicable: -->
- Linear issue:
- Slack thread:

## Checklist
<!-- Put an 'x' in all boxes that apply -->
- [x] I have read the [contributing guidelines](README.md)
- [x] I have tested my changes locally using `docs dev`
- [x] All code examples have been tested and work correctly
- I have gotten approval from the relevant reviewers

Signed-off-by: ChengZi <chen.zhang@zilliz.com>

Author: zc277584121

src/oss/python/integrations/retrievers/index.mdx

@@ -103,7 +103,6 @@ The below retrievers will search over an external index (e.g., constructed from
 <Card title="You.com" icon="link" href="/oss/integrations/retrievers/you-retriever" arrow="true" cta="View guide" />
 <Card title="Zep Cloud" icon="link" href="/oss/integrations/retrievers/zep_cloud_memorystore" arrow="true" cta="View guide" />
 <Card title="Zep Open Source" icon="link" href="/oss/integrations/retrievers/zep_memorystore" arrow="true" cta="View guide" />
-<Card title="Zilliz Cloud Pipeline" icon="link" href="/oss/integrations/retrievers/zilliz_cloud_pipeline" arrow="true" cta="View guide" />
 <Card title="Zotero" icon="link" href="/oss/integrations/retrievers/zotero" arrow="true" cta="View guide" />
 </Columns>