RFR: JDK-8292073: NMT: remove unused constructor parameter from MallocHeader

[Thomas Stuefe]

Trivial cleanup, removes an unused parameter from `MallocHeader` ctor

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Commit messages:
 - JDK-8292073-NMT-remove-unused-constructor-parameter-from-MallocHeader

Changes: https://git.openjdk.org/jdk/pull/10314/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10314&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292073
  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10314.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10314/head:pull/10314

PR: https://git.openjdk.org/jdk/pull/10314