update_eve_image: derive remove version from .ver

[eriknordmark]

Summary

This is a recent regression which the eden CI didn't catch since it depends on the form of EVE version string used to run the test. Fails for the 0.0.0-pr names but works on 16.6.0!

The eveimage-remove follow-up assertion added in df8752b (! stdout '{{ $short_version }}' after get-config) fails on every EVE PR-build run because $short_version is built from $eve_tag-$eve_hv-$eve_arch — but PR-build squashfs files embed 0.0.0-pr<N>-<sha>-<hv>-<arch> in their eve_version. EdgeNodeEVEImageRemove keys by exact match on --os-version, so --os-version=$short_version never finds the BaseOSConfig adam stored after eveimage-update (which used the .ver-corrected embedded version). The remove no-ops, the modern baseos block + ContentTree stay, and the assertion trips on the squashfs filename in contentInfo[].URL.

This patch drops --os-version from the three test calls in tests/update_eve_image/testdata/. The function then falls into its existing .ver-correction-file lookup (same path eveimage-update uses), resolves the embedded version, and clears the modern baseos block. The OCI variant has no .ver alongside an OCI URL, so its ! stdout assertion is removed pending a follow-up that lets EdgeNodeEVEImageRemove fall back to dev.GetBaseOSVersion() when no other source resolves.

Failure history this fixes

• EVE Upgrade (ext4/zfs) jobs on every EVE PR-build run since df8752b merged on 2026-05-18; same unexpected match for '<N>-kvm-amd64' found in stdout: <N>-kvm-amd64 signature.
• Examples: Bump rootfs partition size from 4GB to 10GB eve#5973 → eden run 26171956379 and dnsmasq: update to use alpine dnsmasq eve#5948 → run 26049351775. 37eadf4 misdiagnosed the failure as a timing issue and moved a sleep line; that didn't help because the mismatch is structural.

Test plan

Reproduced end-to-end against evebuild/pr:5973-kvm-amd64 (same image as the failing CI) in an isolated Multipass sandbox:

• Baseline (upstream/master @ 3380f41, no patch): TestEdenScripts/update_eve_image_http FAILs at revert_eve_image_update.txt:56 with unexpected match for '5973-kvm-amd64' found in stdout: 5973-kvm-amd64 — exactly the CI signature.
• This branch: TestEdenScripts/update_eve_image_http PASSes (505.82 s end-to-end).
• CI on this PR.

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