Deprecate 16 Resource pages

## Goal
We would like to deprecate the following solutions pages because they have no meaningful traffic from any source and no backlinks.

|  Pages to Deprecate                                                    |
|------------------------------------------------------------------------------------------------|
| https://about.gitlab.com/resources/demo-agile-delivery/                                    |
| https://about.gitlab.com/resources/ebook-agile-culture-techniques/                         |
| https://about.gitlab.com/resources/ebook-agile-delivery-models/                            |
| https://about.gitlab.com/resources/ebook-dev-guide-app-security/                           |
| https://about.gitlab.com/resources/ebook-guide-remote-devops/                              |
| https://about.gitlab.com/resources/gitlab-vs-atlassian/                                    |
| https://about.gitlab.com/resources/video-gitlab-security-demo/                             |
| https://about.gitlab.com/resources/video-going-cloud-native/                               |
| https://about.gitlab.com/resources/video-security-capabilities/                            |
| https://about.gitlab.com/resources/whitepaper-agile-iteration/                             |
| https://about.gitlab.com/resources/whitepaper-bridging-the-divide/                         |
| https://about.gitlab.com/resources/whitepaper-DevSecOps-Proactive-security-reduce-risk/    |
| https://about.gitlab.com/resources/whitepaper-exec-briefing-series-digital-transformation/ |
| https://about.gitlab.com/resources/whitepaper-planning-for-success/                        |
| https://about.gitlab.com/resources/whitepaper-speed-to-mission/                            |
| https://about.gitlab.com/resources/whitepaper-whats-your-digital-readiness/                |

These pages were defined in the [IA Refresh Content Audit](https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/354). You can find them in the [Cleaned audit - Phase 1 - website refresh spreadsheet](https://docs.google.com/spreadsheets/d/1fCyFV8gHQrE2EWDZNr801RMJiPTIIG-Wcrvd_sPadSM/edit#gid=116929303) in the "Delete" sheet. 

### Jobs To Be Done
* **Situation**: *Pages listed above to removed from the marketing site and if a user hits that URL, they are presented with a 404 page*
* **Motivation**: *We want to reduce the number of pages in the marketing site*
* **Outcome**: *So we can be efficient*

## DCI
[DRI, Consulted, Informed](https://about.gitlab.com/handbook/people-group/directly-responsible-individuals/#dri-consulted-informed-dci)

- [ ] DRI: `TBD`
- [ ] Consulted: @laurenbarker @hsmith-watson 
- [ ] Informed: `Everyone`

## In scope
What is within scope of this request?

- [x] Remove the listed pages. They most likely exist in the www-gitlab-com repository.
- [ ] Mark the pages as "complete" in the [Cleaned audit - Phase 1 - website refresh spreadsheet] once removed

## Requirements
What are the requirements for this request? Checklist below is an example of common requirements, please check all that apply and adjust as necessary:

- [ ] Copy writing
- [ ] Illustration
- [ ] Custom Graphics
- [ ] Research
- [ ] Data / Analytics
- [ ] UX Design
- [x] Engineering

Story points: 2.0