Removing dead code from our copy of Xalan.

The trace package isn't accessible via our public API, so I've removed it.
Exception localization isn't worthwhile.
The Exslt code is a third-party extension that isn't necessary for the spec.
Several other classes and methods were unused; I used IntelliJ to find and remove these.

There's more that can go, but this is a fine first step.
166 files changed