Fix Provides in python3 subpackage

PyCryptodome is a self-contained Python package of low-level cryptographic primitives.

PyCryptodome is a fork of PyCrypto. It brings the following enhancements with respect to the last official version of PyCrypto (2.6.1):

• Authenticated encryption modes (GCM, CCM, EAX, SIV, OCB)
• Accelerated AES on Intel platforms via AES-NI
• Elliptic curves cryptography (NIST P-256 curve only)
• Better and more compact API (nonce and iv attributes for ciphers, automatic generation of random nonces and IVs, simplified CTR cipher mode, and more)
• SHA-3 (including SHAKE XOFs) and BLAKE2 hash algorithms
• Salsa20 and ChaCha20 stream ciphers
• scrypt and HKDF
• Deterministic (EC)DSA
• Password-protected PKCS#8 key containers
• Shamir's Secret Sharing scheme
• Random numbers get sourced directly from the OS (and not from a CSPRNG in userspace)
• Cleaner RSA and DSA key generation (largely based on FIPS 186-4)
• Major clean ups and simplification of the code base

PyCryptodome is not a wrapper to a separate C library like OpenSSL. To the largest possible extent, algorithms are implemented in pure Python. Only the pieces that are extremely critical to performance (e.g. block ciphers) are implemented as C extensions.