RFR: 8253029: [PPC64] Remove obsolete Power6 code

[David Holmes]

On Thu, 10 Sep 2020 19:52:08 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> The recent PPC64 platform files still contain code which is part of a Power6 optimization called Power6Scheduler.
> However, this functionality was never completely contributed so it was never usable in the OpenJDK. We should remove it
> since we're no longer optimizing for Power6.

Code changes seem fine but this will need a CSR request as the flags are product flags. The CSR request can argue for
immediate obsoletion (will need to be added to flags table in arguments.cpp) or even expiry (as per current webrev).

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/116