Remove ubuntu OVAL importer and set remove dupe advisories to run as once

Signed-off-by: Tushar Goel <tushar.goel.dav@gmail.com>

Author: TG1999

vulnerabilities/importers/ubuntu.py

@@ -18,6 +18,7 @@ class RemoveDuplicateAdvisoriesPipeline(VulnerableCodePipeline):
     """Pipeline to compute new advisory content id and remove duplicate advisories based on their content."""
 
     pipeline_id = "remove_duplicate_advisories"
+    run_once = True
 
     @classmethod
     def steps(cls):