charon-tkm: Use built-in plugins instead of OpenSSL

charon-tkm: Use built-in plugins instead of OpenSSL

Since the encryption has been moved into the TKM we don't rely on many
cryptographic operations.  Mainly SHA-1 that's used in IKEv2 (NAT-D) and
for some internal hashes (cookies, message duplicate detection), and
certificate and public key parsing (not the actual signature/chain
verification, which is done by the TKM).