Delete from Multiple Tables using db_delete()
You can't I'm afraid.

db_delete() takes a single string parameter to define which table the query is to be run against. There's no scope to provide more than one table at a time.

You can run any SQL statement you like, though, with db_query(), eg.

// Deletes all nodes and related author users...please don't actually run this!!
$sql = 'DELETE u, n FROM {node} n INNER JOIN {users} u ON u.uid = n.uid';
db_query($sql);