backups: no need to track taskId, we track it in task.type+prefix

migrations/schema.sql

@@ -313,11 +313,9 @@ CREATE TABLE IF NOT EXISTS backupTargets(
     format VARCHAR(16) NOT NULL,
     schedule VARCHAR(128),
     priority BOOLEAN DEFAULT false, // only because 'default' and 'primary' are reserved keywords
-    taskId INTEGER, // current task
     creationTime TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
     ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
 
-    FOREIGN KEY(taskId) REFERENCES tasks(id),
     PRIMARY KEY (id)
 );