Remove thumbnail generation from process

Closes #1715 (closed)

arkindex/process/serializers/imports.py

@@ -474,12 +474,7 @@ class StartProcessSerializer(serializers.Serializer):
                 )
 
         else:
-            if validated_data.get("worker_activity"):
-                errors["worker_activity"].append("The process must have workers attached to handle their activity.")
-            if validated_data.get("use_cache"):
-                errors["use_cache"].append("The process must have workers attached to use cached results.")
-            if validated_data.get("use_gpu"):
-                errors["use_gpu"].append("The process must have workers attached to use GPUs.")
+            errors["__all__"].append("The process must have worker runs to be started.")
 
         if errors:
             raise ValidationError(errors)