[Stale Content] Delete FederalRegister.gov API case study — describes 2012 v1 API

## What needs to change
The FederalRegister.gov API case study is a 2012 PDF describing the first version of the Federal Register API. The API has evolved significantly since then and the case study no longer reflects how the API works. The link to the PDF also returns errors intermittently. This case study should be removed.

## Where to find it
Navigate to `pages/_summaries/` and find the file linking to:
```
https://www.federalregister.gov/uploads/2012/11/FR2-API-Case-Study1.pdf
```
Search if needed:
```
grep -r "FR2-API-Case-Study\|FederalRegister.*API.*case" pages/_summaries/
```

## Before deleting
Confirm nothing else in the repo links to this file:
```
grep -r "federalregister.*case-study\|fr2-api" pages/
```

## How to verify
Visit https://resources.data.gov/categories/case-studies-examples and confirm the FederalRegister.gov API case study no longer appears in the listing.