Remove server-side HelloVerifyRequest support.

I found no users of this. We can restore it if needbe, but I don't expect
anyone to find it useful in its current form. The API is suspect for the same
reasons DTLSv1_listen was. An SSL object is stateful and assumes you already
have the endpoint separated out.

If we ever need it, server-side HelloVerifyRequest and DTLSv1_listen should be
implemented by a separate stateless listener that statelessly handles
cookieless ClientHello + HelloVerifyRequest. Once a ClientHello with a valid
cookie comes in, it sets up a stateful SSL object and passes control along to
that.

Change-Id: I86adc1dfb6a81bebe987784c36ad6634a9a1b120
Reviewed-on: https://boringssl-review.googlesource.com/3480
Reviewed-by: Adam Langley <agl@google.com>
11 files changed