Revert "libsnapshot: Require snapuserd in CreateUpdateSnapshots()."

This reverts commit d5b5404d.

Reason for revert: There are snapshot related errors while applying 16KB OTA. https://b.corp.google.com/issues/439515487#comment4. Creating revert to see if this is the breaking change. 
Bug: 416748567

Change-Id: Ia8eb595170a9ec2b74ea388efec17c77aacfd001