RFR: 8295861: get rid of list argument in debug agent's removeNode() API

[Chris Plummer]

Get rid of `list` argument in debug agent's `removeNode()` API. The list is stored in the node, so no need to pass it in.

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Commit messages:
 - Remove list argument from removeNode()

Changes: https://git.openjdk.org/jdk/pull/11101/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11101&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295861
  Stats: 7 lines in 1 file changed: 1 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/11101.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11101/head:pull/11101

PR: https://git.openjdk.org/jdk/pull/11101