Fix interval SQL builtin

src/qir/visitor/QIRSQLStringVisitor.java

@@ -151,13 +151,8 @@ public final class QIRSQLStringVisitor implements IQIRVisitor<String> {
         }
         if (curr instanceof QIRBuiltin) {
             final String name = ((QIRBuiltin) curr).name;
-            if (name.equals("date"))
+            if (name.equals("date") || name.equals("interval"))
                 return name + " " + args.stream().map(arg -> arg.accept(this)).collect(Collectors.joining(" "));
-            if (name.equals("interval")) {
-                final String expr = args.pop().accept(this);
-                final String format = args.pop().accept(this);
-                return name + " " + expr + " " + format.substring(1, format.length() - 1);
-            }
             if (name.equals("count") && args.size() == 0)
                 return "count(*)";
         }