Fix QMTest reference filename lookup
BaseTest.GetPlatform
was modified (why?) with !986 (merged) (originally in
127ebab4), which breaks the lookup of
platform-specific reference filenames in QMTests.
The effect can be seen in the avx2 builds, e.g. in the Gaudi tests.
This MR reverts the change and hopefully fixes the test logic. An unused function is also removed.