Using `RelBuilder.create` without a schema

[Aryeh Hillman]

Is there a way to use `RelBuilder.create` without a schema?

example:

```
    RelBuilder relBuilder =
RelBuilder.create(Frameworks.newConfigBuilder().build());
    RelNode relNode = relBuilder.scan("s1", "t1")
        .filter(relBuilder.equals(relBuilder.field("f1"),
relBuilder.literal("1")))
        .project(relBuilder.field("a"), relBuilder.field("b"))
        .build();
```

(understandably) blows up with `Exception in thread "main"
org.apache.calcite.runtime.CalciteException: Table 's1.t1' not found`

warmly,
aryeh