RHINENG-20474: don't mark uploaded system as stale

fixup for af7359f
fixing:
{"@timestamp":"2025-09-11T03:36:30.914Z","err":"unable to process upload\nsaving system into the database: Unable to save or update system in database: unable to update system_platform: fatal error restarting pod\ndatabase error\nERROR: deadlock detected (SQLSTATE 40P01)","level":"panic","message":"Handler failed"}

Author: MichaelMraka

listener/upload.go

@@ -357,7 +357,6 @@ func updateSystemPlatform(tx *gorm.DB, accountID int, host *Host,
 	var colsToUpdate = []string{
 		"display_name",
 		"last_upload",
-		"stale",
 		"stale_timestamp",
 		"stale_warning_timestamp",
 		"culled_timestamp",