refactor(ansible): delete .env files and update README references

[xmfcx]

• Parent issue: refactor(ansible): move version pins from .env files to ansible role defaults #6938
• Delete amd64.env, amd64_jazzy.env, and arm64.env now that all consumers have been removed
• Remove amd64.env from .webauto-ci.yaml key_files
• Update manual installation instructions in 5 ansible role READMEs to extract versions from defaults/main.yaml instead of sourcing the deleted files

Why

This is the final step of the .env file removal tracked in #6938. All consumers were already migrated in prior PRs:

• refactor(ansible): add version defaults to role defaults #6939, refactor(ansible): rename cumm_version to spconv_cumm_version #6940 (Phase 1: added ansible role defaults)
• refactor(ansible): remove rmw_implementation_name from playbook vars #6947 (ansible playbooks)
• refactor: stop sourcing .env files in shell scripts #6949 (shell scripts)
• refactor(docker): derive image names from rosdistro, remove env COPY #6950 (docker)
• refactor(ci): pass rosdistro instead of env files to workflows #6952, refactor(ci): convert load-env workflow to derive-image-names composite action #6961 (CI workflows)

With every consumer rewired, the .env files are dead code. Deleting them completes the migration to ansible role defaults as the single source of truth for version pins.

---

• Depends on refactor(ci): convert load-env workflow to derive-image-names composite action #6961 (already merged)
• Follow-up needed in autoware-documentation repo to update the CUDA version link in troubleshooting docs

Test plan

• CI passes -- no workflow, script, or Dockerfile references the deleted files
  • https://github.com/autowarefoundation/autoware/actions/runs/23717186526
• Grep confirms no remaining references: git grep -E 'amd64\.env|amd64_jazzy\.env|arm64\.env' returns nothing
• setup-dev-env.sh --ros-distro humble still runs (uses --extra-vars rosdistro=... only, no .env sourcing)
• docker/build.sh --ros-distro humble still runs (uses derive_images(), no .env sourcing)

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[oguzkaganozt]

LGTM