Java: `Nullness.unboxed` does not use `ConversionSite`

The private predicate `unboxed` of `semmle.code.java.dataflow.Nullness` seems to match locations where an implicit conversion from boxed to primitive type occurs:
https://github.com/github/codeql/blob/a7030c7fed4811f63c70d8fe67941f67b045b3aa/java/ql/src/semmle/code/java/dataflow/Nullness.qll#L54

Would it maybe be better to use `ConversionSite` of `semmle.code.java.Conversions` for this to avoid code duplication, or was this done intentionally (for performance reasons)?