sun.misc.Cleaner has been moved to internal package jdk.internal.ref recently [1] to clean-up sun.misc namespace. But now that:

- we have comparable public API (java.lang.ref.Cleaner & Cleanable) [2]
- we have an internal shared java.lang.ref.Cleaner instance (jdk.internal.ref.CleanerFactory.cleaner())
- sun.misc.Cleaner is not a special kind of Reference any more in the JVM [3]
- threads failing to allocate memory in NIO themselves get involved in cleaning, see JDK-6857566

...I think there's no reason to keep this special internal API any more. It can be replaced with public API.

I propose to remove jdk.internal.ref.Cleaner class and replace its usages with java.lang.ref.Cleaner and friends [4].

[1] https://bugs.openjdk.java.net/browse/JDK-8148117
[2] https://bugs.openjdk.java.net/browse/JDK-8138696
[3] https://bugs.openjdk.java.net/browse/JDK-8143847
[4] http://cr.openjdk.java.net/~plevart/jdk9-dev/removeInternalCleaner/webrev.03/