RFR: 8301217: Remove FilteringClosure

[Albert Mingkun Yang]

Simple removing redundant code.

Test: tier1-5

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Commit messages:
 - walk-mem

Changes: https://git.openjdk.org/jdk/pull/12243/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12243&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301217
  Stats: 99 lines in 7 files changed: 0 ins; 72 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/12243.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12243/head:pull/12243

PR: https://git.openjdk.org/jdk/pull/12243