crypto: delete stubs

Crypto is a package that comes from pycrypto, which was last updated in
2013. It proudly supports Python 2.1 through 3.3.
There's a near drop-in replacement from pycryptodome, which seems well
maintained. pycryptodome has provided stubs for the last two years.

I propose we get rid of the whole thing. pycrypto seems about as dead as
software can get. These stubs have received two fixes since 2016.

#2952
https://pycryptodome.readthedocs.io/en/latest/src/vs_pycrypto.html
https://github.com/Legrandin/pycryptodome/blob/master/Changelog.rst#371-25-november-2018

Author: hauntsaninja