Device table: remove references to the worker state
Device table: remove references to the worker state

This will be removed soon and decrease the number of database queries by ~20%.

Change-Id: Iff1b537a65c3eef10c92ba0deace230fe53ed7cb

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server