RFR: 8275800: Redefinition leaks MethodData::_extra_data_lock

[Coleen Phillimore]

The Mutex destructor isn't called for the MDO lock.  We found this leak with crashes for the patch to print all mutex locks on error, which is now withdrawn.  It was easily reproduced with that patch.  It is not easily reproduced otherwise.
I tested this change with that patch though and it passes tier1-6,

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Commit messages:
 - 8275800: Redefinition leaks MethodData::_extra_data_lock

Changes: https://git.openjdk.java.net/jdk/pull/6105/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6105&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275800
  Stats: 17 lines in 2 files changed: 8 ins; 8 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6105.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6105/head:pull/6105

PR: https://git.openjdk.java.net/jdk/pull/6105