Remove the configuration to enable weak ciphersuites in SSL / TLS

This does not affect users who use the default config.h, as this option was already off by default.

If you were using a weak cipher, please switch to any of the modern, recommended ciphersuites (based on AES-GCM, AES-CCM or ChachaPoly for example) and if your peer doesn't support any, encourage them to upgrade their software.

If you were using a ciphersuite without encryption, you just have to enable MBEDTLS_CIPHER_NULL_CIPHER now.