RFR: 8286387: Remove unused FreeListAllocator::reduce_free_list

[Albert Mingkun Yang]

Simple change of removing an unused API.

Test: tier1

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Commit messages:
 - remove

Changes: https://git.openjdk.java.net/jdk/pull/8594/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8594&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286387
  Stats: 38 lines in 5 files changed: 0 ins; 38 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8594.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8594/head:pull/8594

PR: https://git.openjdk.java.net/jdk/pull/8594