Remove SSL_set_session_secret_cb (EAP-FAST)

This is only used for EAP-FAST which we apparently don't need to support.
Remove it outright. We broke it in 9eaeef81fa2d4fd6246dc02b6203fa936a5eaf67 by
failing to account for session misses.

If this changes and we need it later, we can resurrect it. Preferably
implemented differently: the current implementation is bolted badly onto the
handshake. Ideally use the supplied callbacks to fabricate an appropriate
SSL_SESSION and resume that with as much of the normal session ticket flow as
possible.

The one difference is that EAP-FAST seems to require the probing mechanism for
session tickets rather than the sane session ID echoing version.  We can
reimplement that by asking the record layer to probe ahead for one byte.

Change-Id: I38304953cc36b2020611556a91e8ac091691edac
Reviewed-on: https://boringssl-review.googlesource.com/2360
Reviewed-by: Adam Langley <agl@google.com>
8 files changed