RFR(xs): 8204663: clean up remaining native parts after JDK-8187631

[Thomas Stüfe]

Hi,

may I please have reviews for this small cleanup.

Bug: https://bugs.openjdk.java.net/browse/JDK-8204663
Webrev: http://cr.openjdk.java.net/~stuefe/webrevs/JDK-8204663-clean-up-after-JDK-8187631/webrev.00/webrev/

This change removes some native functions from FOS/FIS which are
orphaned and unused since "JDK-8187631: Refactor FileDescriptor close
implementation".

Tests on jdk-submit came back clean save one strange test error on
windows which I cannot reproduce locally. I am investigating that one.

Thank you, Thomas