Drop dead `ENVIRON` and `DATABASE` env vars from stage Terraform

## Context

The dev-side sweep that landed in #747 dropped four dead env vars from `dev/dev.env.example` (`MODE`, `DEVTOOL`, `ENVIRON`, `DATABASE`). Two of those (`ENVIRON`, `DATABASE`) are also still injected into the deployed stage container by Terraform in the [`incubator`](https://github.com/hackforla/incubator) repo. Removing them in CTJ has no effect on stage until they're also removed there.

## Scope

In the `incubator` repo at [`terraform/projects/civic-tech-jobs/environment-stage.tf`](https://github.com/hackforla/incubator/blob/main/terraform/projects/civic-tech-jobs/environment-stage.tf), inside the `container_environment` list of the `civic_tech_jobs_fullstack_stage_service` module call:

```hcl
{ "name" : "ENVIRON", "value" : "stage" },
{ "name" : "DATABASE", "value" : module.civic_tech_jobs_stage_database.database },
```

Drop both entries. No application-side change required - these values are unread in the codebase. Verified by repo grep on the CTJ side; same vars dropped from `dev/dev.env.example` in #747.

`DATABASE` duplicates `SQL_DATABASE`, which Django settings actually consumes.

## References

- CTJ-side dev sweep that paired with this: #747
- ADR-0001 (tooling baseline) describes the env-var hygiene posture: [`docs/decisions/0001-tooling-baseline.md`](../../docs/decisions/0001-tooling-baseline.md)

## Owner

TBD - pending DevOps CoP discussion.