RFR: 8273675: Remove unused Universe::_verify_in_progress flag

[Coleen Phillimore]

This is a trivial change to remove an unused flag in class Universe.
Tested with tier1 on Oracle platforms.

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Commit messages:
 - 8273675: Remove unused Universe::_verify_in_progress flag

Changes: https://git.openjdk.java.net/jdk/pull/5501/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5501&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273675
  Stats: 13 lines in 2 files changed: 0 ins; 13 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5501.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5501/head:pull/5501

PR: https://git.openjdk.java.net/jdk/pull/5501