Manage Elastic Defend section cleanup (#441)

Cleans up lift-and-shift pages in the Solutions and use cases > Security
> Manage Elastic Defend section.
Removes raw migrated files for the cleaned-up pages since they're not
used elsewhere.

Previews:

- [Manage Elastic
Defend](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend)
- [Optimize Elastic
Defend](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend/optimize-elastic-defend)
- [Event capture and Elastic
Defend](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend/event-capture-elastic-defend)
- [Endpoint protection
rules](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend/endpoint-protection-rules)
- [Identify antivirus software on your
hosts](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend/identify-antivirus-software-on-hosts)
- [Allowlist Elastic Endpoint in third-party antivirus
apps](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend/allowlist-elastic-endpoint-in-third-party-antivirus-apps)
- [Elastic Endpoint self-protection
features](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/441/solutions/security/manage-elastic-defend/elastic-endpoint-self-protection-features)

Author: natasha-moore-elastic