chore: fix release workflow configuration

[achou11]

Fixes #359

Noticed an error about missing a build npm script: https://github.com/digidem/mapeo-core-next/actions/runs/6882793274/job/18722037582#step:3:164

npm ERR! Missing script: "build"

Not entirely sure what the necessary change is, but figured at least removing the step that fails would be a good start.

[gmaclennan]

Yes, that should fix it. The necessary build step for npm is in the prepack script, which will automatically run when the package is packed for publishing, so removing the line here should just fix it.