RFR: 8260582: Clean up MacOSFlags implementation

[Ajit Ghaisas]

Changes -
- Its path has two "macos" directories. Last one is removed as MacOSFlags.java is the only file in it. File is moved one directory up.

- Removed unused native method --> it results in undoing the changes in AWTView.m so that it becomes the same as in openjdk/jdk

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Commit messages:
 - clean MacOSFlags.java

Changes: https://git.openjdk.java.net/lanai/pull/162/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=162&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260582
  Stats: 27 lines in 3 files changed: 0 ins; 24 del; 3 mod
  Patch: https://git.openjdk.java.net/lanai/pull/162.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/162/head:pull/162

PR: https://git.openjdk.java.net/lanai/pull/162