RFR [11] 8058965 : Remove IPv6 support from TwoStacksPlainSocketImpl [win]

[Ivan Gerasimov]

Hello!

On Windows we have two different implementations of java.net.Socket:  
DualStackPlainSocketImpl and TwoStacksPlainSocketImpl.
Former is used by default, and the later is only used when the system 
option java.net.preferIPv4Stack is set to "true".
In particular, this means that TwoStacksPlainSocketImpl is never used 
for IPv6, which effectively makes all the IPv6-related code in this 
class dead.
Let's remove this dead code!

The proposed patch mostly consists of code removals.
The changes were verified by existing regression tests:  No failures 
noticed.
I do not propose to change the file name for two reasons:  1) 
simplifying the review,  2) there are plans for further refactoring in 
this area, which will include the file renaming.

Would you please help review the fix?

Bug: https://bugs.openjdk.java.net/browse/JDK-8058965
Webrev: http://cr.openjdk.java.net/~igerasim/8058965/00/webrev/

Thanks in advance!

-- 
With kind regards,
Ivan Gerasimov