SE-0344: Fix example code for `remoteCall`
SE-0344: Fix example code for `remoteCall`

The example code makes a reference to `Res.self`, which is not declared anywhere. From context and from sample code provided by the toolchain, it makes sense that `Res` is the third generic argument of the function, which here is named as `Success`. This example snippet is updated accordingly.
apple/swift-evolution,apple/swift-evolution