RFR: 8282120: optimal capacity tests and test library need to be cleaned up

[Stuart Marks]

The test `java/lang/Enum/ConstantDirectoryOptimalCapacity.java` was problem-listed by [JDK-8281631](https://bugs.openjdk.java.net/browse/JDK-8281631) and essentially superseded by [JDK-8186958](https://bugs.openjdk.java.net/browse/JDK-8186958). Given this, the test should simply be removed. This test is the only test that depends on a test library utility `test/lib/jdk/test/lib/util/OptimalCapacity.java` which has a number of issues of its own, so it should simply be removed as well.

See the bug report, in particular the comment

https://bugs.openjdk.java.net/browse/JDK-8282120?focusedCommentId=14489450&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14489450

for detailed discussion.

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Commit messages:
 - Remove test Enum/ConstantDirectoryOptimalCapacity, utility, and problem list entry.

Changes: https://git.openjdk.java.net/jdk/pull/8303/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8303&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282120
  Stats: 355 lines in 3 files changed: 0 ins; 355 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8303.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8303/head:pull/8303

PR: https://git.openjdk.java.net/jdk/pull/8303