RFR: 8252888: Simplify G1MMUTracker class hierarchy

Fri Sep 18 18:47:43 UTC 2020

On Wed, 16 Sep 2020 23:19:56 GMT, John Tortugo <github.com+2249648+JohnTortugo at openjdk.org> wrote:

> Relates to: https://bugs.openjdk.java.net/browse/JDK-8252888
> Tested on: x86_64 - Linux - tier1
> Need sponsor: yes
> 
> Merge `G1MMUTracker` and `G1MMUTrackerQueue` into a single class and make method members non virtual.

I think it's better to use `G1MMUTracker` as the type name and mention its queue implementation in the comments,
instead of including "Queue" in its name.

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PR: https://git.openjdk.java.net/jdk/pull/214