Replace or remove restartable ECP in ssl_client2.c

[davidhorstmann-arm]

Part of implementing #9904

The program ssl_client2.c uses only a single function from the legacy crypto API

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if (opt.ec_max_ops != DFL_EC_MAX_OPS) {
        mbedtls_ecp_set_max_ops(opt.ec_max_ops);
    }
#endif

This configures the legacy restartable ECP interface.

This task consists of:

• Figuring out whether this legacy call can be replaced with a PSA call
• If it can, replace with PSA
• If it can't, remove the ec_max_ops option from ssl_client2

This task is done when ssl_client2 no longer calls mbedtls_ecp_set_max_ops() (or any other legacy function).

Estimate: 3 Ideal Engineering Hours