AFAIK unused layouts and event sheets are negligible in terms of download size, and since they aren't loaded they wouldn't have any cpu, gpu, or memory overhead for the end user. Unless you've got huge amounts of unused sprite objects/textures that you don't want accessible, then not much you can do besides set up a good file versioning system in your workflow.
Basically even if had the option to choose not to export a specific layout, the assets of a project are global and would be included in the file size regardless of what layout they are used in.