Do not eval importChangesets in 'src batch exec'
Created by: mrnugget
This is part of https://github.com/sourcegraph/sourcegraph/issues/25962 and fixes a bug where a batch spec would end up with too many (duplicated) changeset specs: each src batch exec
invocation evaluated the importChangesets
part again. But since we do that on the server-side with SSBC we don't have to do this in src-cli
at all.