Implement the client side of proposal 198

Implement the client side of proposal 198

This is a feature removal: we no longer fake any ciphersuite other
than the not-really-standard SSL_RSA_FIPS_WITH_3DES_EDE_CBC_SHA
(0xfeff).  This change will let servers rely on our actually
supporting what we claim to support, and thereby let Tor migrate to
better TLS ciphersuites.

As a drawback, Tor instances that use old openssl versions and
openssl builds with ciphers disabled will no longer give the
"firefox" cipher list.