RFR: 8340359: Remove javax.naming.Context.APPLET

[Aleksei Efimov]

JNDI dependency on the `java.applet.Applet` has been removed in JDK9 with [JDK-8051422](https://bugs.openjdk.org/browse/JDK-8051422). It made the `Context.APPLET` environment property obsolete and to be ignored when `javax.naming.InitialContext` is created.

The proposed change removes `javax.naming.Context.APPLET` constant and the tests using it.

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Commit messages:
 - 8340359: Remove javax.naming.Context.APPLET

Changes: https://git.openjdk.org/jdk/pull/22521/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22521&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340359
  Stats: 138 lines in 3 files changed: 0 ins; 137 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22521.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22521/head:pull/22521

PR: https://git.openjdk.org/jdk/pull/22521