RFR: 8367987: Memory leak in MemBaseline: Must delete _vma_allocations

[Johan Sjölen]

Hi,

I forgot to add a destructor which deletes the `_vma_allocations` for JDK-8367249. This PR rectifies this mistake.

Thank you.

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Commit messages:
 - Delete the VMA allocations by the end

Changes: https://git.openjdk.org/jdk/pull/27364/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27364&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367987
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27364.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27364/head:pull/27364

PR: https://git.openjdk.org/jdk/pull/27364