[Speed] performance: remove "pure python" pickle benchmarks?

[Victor Stinner]

Hi,

In benchmarks slower in Python 3.7 compared to 2.7 at
https://speed.python.org/comparison/ I found pickle_pure_python and
unpickle_pure_python. These benchmarks test the pure Python
implementation of the pickle protocol.

I don't see the point of testing the pure Python implementation, since
the C accelerator (_pickle) is always used by default in Python 3. I
propose to remove this benchmark. What do you think?

Victor