ASV: remove duplicated SelectDtypes benchmark
https://github.com/pandas-dev/pandas/pull/36839 added an extensive benchmark class for `select_dtypes` (`dtypes.py::SelectDtypes`), but we actually already had a benchmark in `frame_methods.py`. Now, the new ones are more extensive, testing multiple dtypes and both include/exclude, instead of only including int, so I think the one in frame_methods can be safely removed to avoid duplication of benchmarks:

https://github.com/pandas-dev/pandas/blob/7b78b730aee122bb7d6e90723c4208da234de19e/asv_bench/benchmarks/dtypes.py#L51-L112
thanks @jorisvandenbossche 