RFR: 8286088: add comment to InstallAsyncExceptionHandshake destructor

[Daniel D.Daugherty]

A trivial fix to add comment to InstallAsyncExceptionHandshake destructor.

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Commit messages:
 - 8286088: add comment to InstallAsyncExceptionHandshake destructor

Changes: https://git.openjdk.java.net/jdk/pull/8522/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8522&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286088
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8522.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8522/head:pull/8522

PR: https://git.openjdk.java.net/jdk/pull/8522