Remove problematic base58 module

A french user reported this:

Avec la dernière version de duniterpy (0.62.0), same avec python 3.8 et 3.9:

AttributeError: module 'duniterpy.key.base58' has no attribute 'b58decode'

Résolu par:

pubkey_byte = base58.Base58Encoder.decode(str.encode(pubkey))
hash = hashlib.sha256(hashlib.sha256(pubkey_byte).digest()).digest()
return base58.Base58Encoder.encode(hash)[:3]

DuniterPy’s base58 module only checks data types. So, not really useful and overrides base58 module. Should be removed to use base58 module instead.