Simplify CI_DEPLOY_FREEZE conditions in Auto DevOps

What does this MR do and why?

Simplifies the CI_DEPLOY_FREEZE conditions in Auto DevOps templates, as discussed in #351928 (closed)

How to validate

Start with the following .gitlab-ci.yml:

stages:
  - test
  - review
  - staging
  - canary
  - production
  - incremental rollout 10%
  - incremental rollout 25%
  - incremental rollout 50%
  - incremental rollout 100%
  - cleanup

include:
  - project: gitlab-org/gitlab
    file: lib/gitlab/ci/templates/Jobs/Deploy.gitlab-ci.yml
    ref: simplify-ci-deploy-freeze-condition

variables:
  KUBECONFIG: placeholder

• When CI_DEPLOY_FREEZE is blank, this should have some jobs.
• When CI_DEPLOY_FREEZE is present, this should not have any jobs.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.