[jdk9] RFR: 8163517: Various cleanup in java.io code

[Ivan Gerasimov]

Hello!

Here's a cleanup pass through the code in java.io package.

Would you please help review?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8163517
WEBREV: http://cr.openjdk.java.net/~igerasim/8163517/00/webrev/

With kind regards,
Ivan