Remove log_uc

* Logs now are attached to receipt, so removing block + index unique
constraint

db/migrations/1516050071_add_log_fk_constraint.down.sql

@@ -6,4 +6,7 @@ ALTER TABLE logs
 ALTER TABLE logs
   DROP COLUMN receipt_id;
 
+ALTER TABLE logs
+  ADD CONSTRAINT log_uc UNIQUE (block_number, index);
+
 COMMIT;

db/migrations/1516050071_add_log_fk_constraint.up.sql

@@ -1,4 +1,6 @@
 BEGIN;
+ALTER TABLE logs
+    DROP CONSTRAINT log_uc;
 
 ALTER TABLE logs
   ADD COLUMN receipt_id INT;