Remove FIPS image Dockerfiles (images/{base,desktop,coder}-fips/)

[ausbru87]

Context

Part of the FIPS-removal effort. See REMOVE_FIPS_PLAN.md for the full plan and premise.

Premise: Coder is not a FIPS boundary component. All traffic entering/leaving the Coder deployment is terminated by upstream load balancers and proxies that perform TLS with FIPS-validated crypto modules. We therefore do not need custom FIPS-mode container images.

Scope

Delete all three custom FIPS workspace/server image directories.

Files to delete

• images/base-fips/ (entire directory — RHEL 9 UBI with update-crypto-policies --set FIPS)
• images/desktop-fips/ (entire directory — XFCE+KasmVNC on top of base-fips)
• images/coder-fips/ (entire directory — Alpine image wrapping the FIPS Coder binary)

If this empties images/, delete the directory too.

Acceptance criteria

• find images/ -type f returns empty (or the directory is removed).
• grep -rin fips images/ 2>/dev/null returns nothing.
• Repo still passes terraform fmt -check -recursive infra/terraform/ and tflint (neither reference these paths, so this should already pass).

Dependencies

None. Logically paired with the FIPS-workflows removal (separate issue), but file sets are disjoint so the two PRs can be worked in parallel.

Notes for downstream issues

After this merges, two GitHub Actions workflows (coder-fips.yml, images.yml) will have dangling paths: filters referencing deleted directories. That is handled by the workflow-removal issue.

[ausbru87]

Part of tracking issue #10.