RFR: 8268902: Testing for threadObj != NULL is unnecessary in suspend handshake

[Coleen Phillimore]

In the last pull request on this topic, I was making more general (mis)statements, but this null threadObj check is only for the case where we're suspending a thread which already has a threadObj.  This null check is unnecessary.
Tested already with tier1-6 (rerun tier1).

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Commit messages:
 - 8268902: Testing for threadObj != NULL is unnecessary in suspend handshake

Changes: https://git.openjdk.java.net/jdk/pull/4598/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4598&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268902
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4598.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4598/head:pull/4598

PR: https://git.openjdk.java.net/jdk/pull/4598