Remove SRP code. It contains a bug (this should not surprise anyone), but
the details are under embargo. The original plan was to wait for the
embargo to lift, but we've been waiting for quite some time, and there's no
indication of when or even if it will end. No sense in dragging this out
any longer.

The SRP code has never been enabled in OpenBSD, though I understand it is
in use by some other people. However, in light of this and other issues,
we're officially saying SRP is outside the scope of libressl. (For now.)