RFR: JDK-8290046: NMT: Remove unused MallocSiteTable::reset()

[Thomas Stuefe]

Trivial cleanup. `MallocSiteTable::reset()` and `MallocSiteTable::delete_linked_list()` are not used anymore since [JDK-8256844](https://bugs.openjdk.org/browse/JDK-8256844). They can be removed.

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Commit messages:
 - Remove MallocSiteTable::reset

Changes: https://git.openjdk.org/jdk/pull/9441/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9441&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290046
  Stats: 26 lines in 2 files changed: 0 ins; 26 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9441.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9441/head:pull/9441

PR: https://git.openjdk.org/jdk/pull/9441