[8u] TLSv1.3 RFR: 8245469: Remove DTLS protocol implementation

[Alexey Bakhtin]

Please review changes required to backport TLSv1.3 protocol from JDK11.0.7 to JDK8u

This is the third part of backport discussed in the thread [1]

JBS task: https://bugs.openjdk.java.net/browse/JDK-8245469
Webrev: http://cr.openjdk.java.net/~abakhtin/tls1.3/8245466/8245469/webrev.v0/

This patch removes DTLS protocol support from TLS implementation.
There are no plans to support DTLS protocol in JDK8u
The patch should be applied after the patch for JDK-8245468

[1] - https://mail.openjdk.java.net/pipermail/jdk8u-dev/2020-May/011664.html

Regards
Alexey