security/py-trezor: drop dependency on blake2

Dependency on external blake2 implementation was dropped since 0.11.5:
https://github.com/trezor/trezor-firmware/blob/main/python/CHANGELOG.md#changed-10

it is now using implementation from python's hashlib module. So just drop it from Makefile.

PR: 277132
Approved by: ehaupt (maintainer)