RFR 8231314: java.time serialization warning cleanup

[Roger Riggs]

Please review code cleanup that will remove the need to suppress soon to 
be introduced
warnings [1] about static typing of serialization related fields.
A few of the implementation Ser classes that serialize java.time types 
are affected.

Webrev:
http://cr.openjdk.java.net/~rriggs/webrev-warn-serializable-8231314/

Thanks, Roger

[1] https://bugs.openjdk.java.net/browse/JDK-8231202