Remove strategy.data.gov from CSP header in meta.html

## Summary

After images are migrated off strategy.data.gov, remove it from the Content Security Policy header in resources.data.gov.

## Background

`pages/_includes/meta.html` includes `https://strategy.data.gov` in the `img-src` directive of the Content Security Policy. Once the image migration in Ticket 2 is complete, this entry is no longer needed and should be removed to keep the CSP tight.

## Task

- [ ] Remove `https://strategy.data.gov` from the `img-src` directive in `pages/_includes/meta.html`

## Acceptance criteria

- [ ] `meta.html` CSP no longer references `strategy.data.gov`
- [ ] No console CSP errors on a preview build

## Depends on

Ticket 2