Remove DHE-PSK key exchange

[gilles-peskine-arm]

Remove the DHE-PSK key exchange.

• Prerequisites:
  • Test cases: none
• Config option: MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED
• Key exchange type: MBEDTLS_KEY_EXCHANGE_DHE_PSK
• Affected cipher suite macros regex: MBEDTLS_TLS_DHE_PSK_\w+
• Full list of cipher suite names: TLS-DHE-PSK-WITH-CHACHA20-POLY1305-SHA256 TLS-DHE-PSK-WITH-AES-256-GCM-SHA384 TLS-DHE-PSK-WITH-AES-256-CCM TLS-DHE-PSK-WITH-AES-256-CBC-SHA384 TLS-DHE-PSK-WITH-AES-256-CBC-SHA TLS-DHE-PSK-WITH-CAMELLIA-256-GCM-SHA384 TLS-DHE-PSK-WITH-CAMELLIA-256-CBC-SHA384 TLS-DHE-PSK-WITH-AES-256-CCM-8 TLS-DHE-PSK-WITH-ARIA-256-GCM-SHA384 TLS-DHE-PSK-WITH-ARIA-256-CBC-SHA384 TLS-DHE-PSK-WITH-AES-128-GCM-SHA256 TLS-DHE-PSK-WITH-AES-128-CCM TLS-DHE-PSK-WITH-AES-128-CBC-SHA256 TLS-DHE-PSK-WITH-AES-128-CBC-SHA TLS-DHE-PSK-WITH-CAMELLIA-128-GCM-SHA256 TLS-DHE-PSK-WITH-CAMELLIA-128-CBC-SHA256 TLS-DHE-PSK-WITH-AES-128-CCM-8 TLS-DHE-PSK-WITH-ARIA-128-GCM-SHA256 TLS-DHE-PSK-WITH-ARIA-128-CBC-SHA256 TLS-DHE-PSK-WITH-NULL-SHA384 TLS-DHE-PSK-WITH-NULL-SHA256 TLS-DHE-PSK-WITH-NULL-SHA

Follow the steps in https://github.com/Mbed-TLS/mbedtls/issues/9681 unless there is a good reason to deviate.