[Stale Content] Delete M-11-06 WikiLeaks memo — narrow event-specific content

## What needs to change
The summary file for OMB M-11-06 (WikiLeaks — Mishandling of Classified Information, 2010) should be removed. This was a narrow event-specific memo issued in response to a single incident. It has no ongoing data governance relevance and does not belong in a federal data resources repository.

## Where to find it
Navigate to `pages/_summaries/` and find the file linking to OMB M-11-06. Search if needed:
```
grep -r "M-11-06\|WikiLeaks" pages/_summaries/
```

## Before deleting
Confirm nothing else in the repo links to this file:
```
grep -r "m-11-06" pages/
```

## How to verify
Visit https://resources.data.gov/categories/guidance and confirm the M-11-06 entry no longer appears.