Core: Drop workarounds for unsupported browsers

One test could be dropped. There is also a `detectDuplicates` one that claims is for Chrome before version 14 but even in current Chrome this test returns `false` (`true` in other browsers). What's going on here?

cc @gibson042
Speaking of, looks like some jQuery flavor made it into the `CLASS` find method (typeof). Let's change that to use `rnative` as well for consistency.