jmx-dev RFR: 8318707: Remove the Java Management Extension (JMX) Management Applet (m-let) feature

[Kevin Walls]

Remove the MLet feature and its tests.

Some tests use MLet classes but are not testing MLets.  These are updated, to use another test MBean or an MBean which is a URLClassLoader, e.g.
test/jdk/javax/management/MBeanServer/PostExceptionTest.java
test/jdk/javax/management/remote/mandatory/loading/TargetMBeanTest.java

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Commit messages:
 - remote old commented-out code
 - Merge remote-tracking branch 'upstream/master' into 8318707_MLet_Remove
 - (C) updates
 - Remove MLet from additional tests
 - Further test updates
 - Addtional test updates
 - Remove PrivateMLet from ClassleakTest, retain stated purpose of test
 - Merge remote-tracking branch 'upstream/master' into 8318707_MLet_Remove
 - Test update
 - remove LibraryLoader MLet test
 - ... and 5 more: https://git.openjdk.org/jdk/compare/a5cf4210...cc6e0d28

Changes: https://git.openjdk.org/jdk/pull/16363/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16363&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318707
  Stats: 3532 lines in 39 files changed: 41 ins; 3429 del; 62 mod
  Patch: https://git.openjdk.org/jdk/pull/16363.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16363/head:pull/16363

PR: https://git.openjdk.org/jdk/pull/16363