RFR: 8291733: Remove JFR events that expose hashtable

[Coleen Phillimore]

There are JFR events for the Placeholders table, LoaderConstraintTable and ProtectionDomainCacheTable. These events expose implementation details for these tables that we'd rather not expose. A users visibility into these tables will not be helpful and it restricts our ability to make these a different (smaller) table or in the case of ProtectionDomain, not a table at all.

The Dictionary table (table of loaded classes) is useful from a users' perspective because it can be resized and we wanted to have events for the resizing. These other tables came along in that change.

Tested with tier1-3.

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Commit messages:
 - 8291733: Remove JFR events that expose hashtable

Changes: https://git.openjdk.org/jdk/pull/9714/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9714&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291733
  Stats: 113 lines in 8 files changed: 0 ins; 111 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9714.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9714/head:pull/9714

PR: https://git.openjdk.org/jdk/pull/9714