Refactor DesktopTestHelpers

Instead of an empty class with a companion object, DesktopTestHelpers
should be simple an object. Furthermore, there is no point is generating
extra java methods that are not used. The overloads may be added later
if those methods are needed in a Java context.

Test: N/A
Flag: EXEMPT (refactoring)
Change-Id: If3c1e65afd2f4349a97b8ed9d8a9732a606373d3