Don't wait for dry at the end of a handshake

For DTLS/SCTP we were waiting for a dry event during the call to
tls_finish_handshake(). This function just tidies up various internal
things, and after it completes the handshake is over. I can find no good
reason for waiting for a dry event here, and nothing in RFC6083 suggests
to me that we should need to. More importantly though it seems to be
wrong. It is perfectly possible for a peer to send app data/alerts/new
handshake while we are still cleaning up our handshake. If this happens
then we will never get the dry event and so we cannot continue.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5084)

ssl/statem/statem_lib.c

@@ -1004,15 +1004,6 @@ WORK_STATE tls_finish_handshake(SSL *s, WORK_STATE wst, int clearbufs, int stop)
     int discard;
     void (*cb) (const SSL *ssl, int type, int val) = NULL;
 
-#ifndef OPENSSL_NO_SCTP
-    if (SSL_IS_DTLS(s) && BIO_dgram_is_sctp(SSL_get_wbio(s))) {
-        WORK_STATE ret;
-        ret = dtls_wait_for_dry(s);
-        if (ret != WORK_FINISHED_CONTINUE)
-            return ret;
-    }
-#endif
-
     if (clearbufs) {
         if (!SSL_IS_DTLS(s)) {
             /*