RFR: 8267752: KVHashtable doesn't deallocate entries

[Coleen Phillimore]

Add a free_entry iteration to the destructor of ~KVHashtables.
Tested with tier1-3.

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Commit messages:
 - 8267752: KVHashtable doesn't deallocate entries

Changes: https://git.openjdk.java.net/jdk/pull/4501/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4501&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267752
  Stats: 20 lines in 1 file changed: 20 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4501.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4501/head:pull/4501

PR: https://git.openjdk.java.net/jdk/pull/4501