RFR: 8261607: SA attach is exceeding JNI Local Refs capacity

[Chris Plummer]

Delete some localrefs to avoid -Xcheck:jni warnings. See CR for details.

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Commit messages:
 - Fix SA -Xcheck:jni warnings and add some testing for the warnings.

Changes: https://git.openjdk.java.net/jdk/pull/2568/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2568&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261607
  Stats: 23 lines in 4 files changed: 16 ins; 3 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2568.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2568/head:pull/2568

PR: https://git.openjdk.java.net/jdk/pull/2568