Docs: Remove reference to removed variables

doc/user/application_security/secret_detection/index.md

@@ -202,8 +202,9 @@ Secret Detection can be customized by defining available CI/CD variables:
 
 | CI/CD variable                    | Default value | Description |
 |-----------------------------------|---------------|-------------|
-| `SECRET_DETECTION_COMMIT_FROM`    | -             | The commit a Gitleaks scan starts at. |
-| `SECRET_DETECTION_COMMIT_TO`      | -             | The commit a Gitleaks scan ends at. |
+| `SECRET_DETECTION_COMMIT_FROM`    | -             | The commit a Gitleaks scan starts at. [Removed](https://gitlab.com/gitlab-org/gitlab/-/issues/243564) in GitLab 13.5. Replaced with `SECRET_DETECTION_COMMITS`. |
+| `SECRET_DETECTION_COMMIT_TO`      | -             | The commit a Gitleaks scan ends at. [Removed](https://gitlab.com/gitlab-org/gitlab/-/issues/243564) in GitLab 13.5. Replaced with `SECRET_DETECTION_COMMITS`. |
+| `SECRET_DETECTION_COMMITS`        | -             | The list of commits that Gitleaks should scan. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/243564) in GitLab 13.5. |
 | `SECRET_DETECTION_EXCLUDED_PATHS` | ""            | Exclude vulnerabilities from output based on the paths. This is a comma-separated list of patterns. Patterns can be globs, or file or folder paths (for example, `doc,spec` ). Parent directories also match patterns. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/225273) in GitLab 13.3. |
 | `SECRET_DETECTION_HISTORIC_SCAN`  | false         | Flag to enable a historic Gitleaks scan. |