RFR 8202154 : Remove unused code in TwoStacksPlainDatagramSocketImpl.c

[Ivan Gerasimov]

Hello!

Some code in TwoStacksPlainDatagramSocketImpl.c is only relevant for 
earlier versions of Windows, which are no longer supported as of JDK 11.
This code can be safely removed.

Also removing an unused argument at 
DualStackPlainDatagramSocketImpl.socketCreate().

Would you please help review this cleanup?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8202154
WEBREV: http://cr.openjdk.java.net/~igerasim/8202154/00/webrev/

Thanks in advance!

-- 
With kind regards,
Ivan Gerasimov