Fix access specifier manipulation in Hex.java

Fortify says we should not modify accessibility:

1. [Hex.java](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/diskstorage/util/Hex.java#L104)

Start with janusgraph-core/src/main/java/org/janusgraph/diskstorage/util/Hex.java at the linked line and inspect how accessibility is being modified. Confirm the intended behavior with the Fortify warning, then make the smallest change that removes the access-specifier manipulation without changing Hex's functionality. Verify the relevant Java checks or tests available in the repository.

Written by the indexing model from the issue text.