[jdk8u] RFR: 8304053: Revert os specific stubs for SystemMetrics [v3]

[Adam Farley]

> This change excludes the duplicated class SystemMetrics, and ensures we use the platform-specific version of the SystemMetrics class instead.

Adam Farley has updated the pull request incrementally with one additional commit since the last revision:

  Removing unix SystemMetrics stub class as well
  
  We shouldn't need it, as jdk8u uses the solaris stub class in the
  same way as it should have used the unix stub class.
  
  Signed-off-by: Adam Farley <adfarley at redhat.com>

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Changes:
  - all: https://git.openjdk.org/jdk8u/pull/40/files
  - new: https://git.openjdk.org/jdk8u/pull/40/files/d4e4f5b9..b6a882fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk8u&pr=40&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk8u&pr=40&range=01-02

  Stats: 31 lines in 1 file changed: 0 ins; 31 del; 0 mod
  Patch: https://git.openjdk.org/jdk8u/pull/40.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u pull/40/head:pull/40

PR: https://git.openjdk.org/jdk8u/pull/40