Refresh and pare down benchmarks game benchmarks

Some of our Benchmark Games [benchmarks](https://github.com/dotnet/performance/tree/master/src/benchmarks/micro/runtime/BenchmarksGame) are a bit old and don't match what they're using now. We also have several copies of 7 of them, which seems wasteful.

* spectralnorm winner is # 5 (uses intrinsics). We should pick that up and drop # 1 and possibly the other.
* k-nucloetide winner is # 1 (uses DictionarySlim). We should probably pick that up and drop the different # 1 that we have and possibly the other.
* binarytrees winner is # 6. We could replace our # 5 with that (both use Task; we also have # 2 that does not and could drop that)
* fannkuch-redux winner is # 9. We could replace our # 5, which is very similar and possibly drop the other too.
* fasta winner is # 5. We probably should replace our our # 2 which is quite different and possibly drop the other.
* Mandelbrot winner is # 9. We could replace our # 7 as it's a progression and possibly drop the other.
* regex-redux # 5 which we already have. We could drop the other one.

I'm not sure what our criteria are for dropping benchmarks but perhaps it would make sense after the 6.0 snap.

cc @AndyAyersMS