Method call to known object should have been reduced

Consider the following program

``` scala
interface Buffer[T] {
def free(): Bool
}

def main() = {
new Buffer[Int] {
def free() = false
}.free()
()
}
```

This results in the following problem in optimized as well as unoptimized LLVM

```
PlainTextError(Method call to known object should have been reduced,None,Error)
```

Also, didn't we want to eliminate PlainTextError?