This change configures Mbed TLS to support the fewest number of things
possible required to run an HTTPS server that caters to the sweet spot
of being legacy enough to support the vast majority of user agents but
modern enough that Chrome and Firefox remain happy. That should entail
- TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
- TLS_RSA_WITH_AES_128_CBC_SHA
Even though other suites still get included so what usually happens in
practice is ECDHE-RSA-AES256-GCM-SHA384 under TLS 1.2 will be selected
and the binary footprint is reasonable, and should cost us about 200kb
