RFR: 8301164: Remove unused ResourceStack class

[Albert Mingkun Yang]

Trivial removing dead code.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/12221/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12221&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301164
  Stats: 33 lines in 2 files changed: 0 ins; 33 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12221.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12221/head:pull/12221

PR: https://git.openjdk.org/jdk/pull/12221