RFR: 8301567: The test/jdk/java/awt/AppContext/ApplicationThreadsStop/java.policy is unused

[Sergey Bylokhov]

The test ApplicationThreadsStop.java was removed by the [JDK-8289616](https://bugs.openjdk.org/browse/JDK-8289616) but the related java.policy was not deleted.

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Commit messages:
 - 8301567: The test/jdk/java/awt/AppContext/ApplicationThreadsStop/java.policy

Changes: https://git.openjdk.org/jdk/pull/12356/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12356&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301567
  Stats: 5 lines in 1 file changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12356.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12356/head:pull/12356

PR: https://git.openjdk.org/jdk/pull/12356