[SIMD] Get rid of the specialized index tests.

Really, we should pass index types through the normal vector tests, not a watered down version. This will compilation time for those tests by quite a bit.

The specialized index tests were introduced because vectorclass is missing functionality for some of its integer vectors, such a devision and bitshift. Partially dune-vectorclass already provides the missing functionality (by way of for-loops), we should just implement it for the remaining stuff too.