Remove default value for CS_DEFAULT_BRANCH_IMAGE

doc/user/application_security/container_scanning/index.md

@@ -134,7 +134,7 @@ You can [configure](#customizing-the-container-scanning-settings) analyzers by u
 | `CI_APPLICATION_REPOSITORY`    | `$CI_REGISTRY_IMAGE/$CI_COMMIT_REF_SLUG` | Docker repository URL for the image to be scanned. | All |
 | `CI_APPLICATION_TAG`           | `$CI_COMMIT_SHA` | Docker repository tag for the image to be scanned. | All |
 | `CS_ANALYZER_IMAGE`            | `registry.gitlab.com/security-products/container-scanning:4` | Docker image of the analyzer. | All |
-| `CS_DEFAULT_BRANCH_IMAGE`      | `$CI_REGISTRY_IMAGE/$CI_DEFAULT_BRANCH:$CI_APPLICATION_TAG"` | The name of the `DOCKER_IMAGE` on the default branch. See [Setting the default branch image](#setting-the-default-branch-image) for more details. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/338877) in GitLab 14.5. | All |
+| `CS_DEFAULT_BRANCH_IMAGE`      | `""` | The name of the `DOCKER_IMAGE` on the default branch. See [Setting the default branch image](#setting-the-default-branch-image) for more details. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/338877) in GitLab 14.5. | All |
 | `CS_DOCKER_INSECURE`           | `"false"`     | Allow access to secure Docker registries using HTTPS without validating the certificates. | All |
 | `CS_REGISTRY_INSECURE`         | `"false"`     | Allow access to insecure registries (HTTP only). Should only be set to `true` when testing the image locally. Works with all scanners, but the registry must listen on port `80/tcp` for Trivy to work. | All |
 | `CS_SEVERITY_THRESHOLD`        | `UNKNOWN`     | Severity level threshold. The scanner outputs vulnerabilities with severity level higher than or equal to this threshold. Supported levels are Unknown, Low, Medium, High, and Critical. | Trivy |