Remove WorkerLightSerializer

Based on !2402 (merged)

Follow up of #1805 (closed)

This serializer was not necessary anymore with light Git references. Only the frontend was implementing a specific behavior to retrieve workers individually.

changed milestone to %Arkindex 1.6.3

requested review from @erouchet

assigned to @vrigal

mentioned in merge request frontend!1757 (merged)

added 3 commits

• 1343ed80 - 1 commit from branch master
• b67dbbf4 - Remove WorkerLightSerializer
• 34b86f49 - Update tests

Compare with previous version

merged