The old Semmle duplicate-code detection code has never been done when
extracting databases for the CodeQL CLI, except that `codeql test run`
will run it _just_ in order to support tests of the feature. With the
sunsetting of Odasa there's no need to even _test_ the feature anymore.
This commit removes those tests that fail when the duplicate-code
detector is turned off. Once it is merged and bumped, we can finally
remove it from `codeql`.
This currently relies on the fact that qltest includes `ql/csharp/ql/src/Metrics` in addition to `ql/csharp/ql/src` on its search path when run internally, which is inconsistent with the other languages. Since this is the only test that relies on it, I'd like to update it and get rid of the extra search root eventually.
