Remove tls_buffer_set_data() and remove/revise callers.

Remove tls_buffer_set_data() and remove/revise callers.

There is no way that tls_buffer_set_data() can currently work in
conjunction with tls_buffer_expand(). This fact is currently hidden by the
way that PHH works, which reads the same data from the record layer (which
it needs to do anyway, since we may not have all of the handshake message
in a single record).

Since this is broken, mop it up and change the PHH callback to not provide
the record data.

ok beck@ tb@