Content folder gets exported twice

Reproduction path:

1. start fresh archetype project
2. in Essentials, install poll plugin
3. rebuild and restart: this will trigger importing XML of the demo poll document, and auto-export will put it into your project.

Expected: the demo poll document gets exported as a separate yaml content source
Actual: the demo poll document also gets exported into the channel's root folder yaml content source, such that, upon bootstrapping a fresh repository, the content bootstrapping runs into a ItemExistsException:

WARN localhost-startStop-1 [JcrContentProcessor.apply:144] Content definition processing failed: polls
[INFO] [talledLocalContainer] javax.jcr.ItemExistsException: Node already exists at path /content/documents/essx/polls
[INFO] [talledLocalContainer] at org.onehippo.cm.engine.JcrContentProcessor.validateAppendAction(JcrContentProcessor.java:109)