refactor(imagemeta): leave the merged containerEnv order to PropertyOrder

Every reader of MergedConfig.ContainerEnvOrder goes through
features.PropertyOrder, which already keeps a key's first position, so
deduplicating it in MergeConfiguration had no effect any test could see.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: aledbf

internal/imagemeta/merge.go

@@ -134,7 +134,6 @@ func MergeConfiguration(entries []Entry) *MergedConfig {
 		}
 	}
 
-	m.ContainerEnvOrder = features.KeyOrder(m.ContainerEnvOrder)
 	m.Mounts = dedupeMountsByTarget(m.Mounts)
 	m.ForwardPorts = dedupeForwardPorts(m.ForwardPorts)
 	m.HostRequirements = mergeHostRequirements(entries)