RFR: 8297310: Remove unimplemented HeapInspection::iterate_over_heap

[Kim Barrett]

Please review this trivial change to remove a function declaration that is never defined.

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Commit messages:
 - remove decl

Changes: https://git.openjdk.org/jdk/pull/11280/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11280&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297310
  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11280.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11280/head:pull/11280

PR: https://git.openjdk.org/jdk/pull/11280