sqldb: remove unused preimage query parameter

sqldb/sqlc/queries/invoices.sql

@@ -47,9 +47,6 @@ WHERE (
 ) AND (
     i.hash = sqlc.narg('hash') OR 
     sqlc.narg('hash') IS NULL
-) AND (
-    i.preimage = sqlc.narg('preimage') OR 
-    sqlc.narg('preimage') IS NULL
 ) AND (
     i.payment_addr = sqlc.narg('payment_addr') OR 
     sqlc.narg('payment_addr') IS NULL