Do not delete background jobs, in case an exception occured

This approach is not valid anymore. It initially was added for jobs
of non existing apps. But jobs of non-existing apps can not be created
so they will never be executed and so this call just catches other
cases which were not intended.

This reverts commit 4f4ad724.

lib/private/backgroundjob/job.php

@@ -54,7 +54,6 @@ abstract class Job implements IJob {
 			if ($logger) {
 				$logger->error('Error while running background job: ' . $e->getMessage());
 			}
-			$jobList->remove($this, $this->argument);
 		}
 	}