[jdk13u-dev] RFR: 8273894: ConcurrentModificationException raised every time ReferralsCache drops referral

[Yuri Nesterenko]

backporting for parity with LTS releases. Clean backport, security tests do pass

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Commit messages:
 - Backport 2166ed136917bb68f8155a25e4f4a6c5c7115566

Changes: https://git.openjdk.org/jdk13u-dev/pull/442/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk13u-dev&pr=442&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8273894
  Stats: 5 lines in 1 file changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk13u-dev/pull/442.diff
  Fetch: git fetch https://git.openjdk.org/jdk13u-dev pull/442/head:pull/442

PR: https://git.openjdk.org/jdk13u-dev/pull/442