RFR: 8359225: Remove unused test/jdk/javax/script/MyContext.java

[Volkan Yazici]

Both `javax/script/PluggableContextTest.java` and its companion `test/jdk/javax/script/MyContext.java` were added in [JDK-6398614](https://bugs.openjdk.org/browse/JDK-6398614). [JDK-8246113](https://bugs.openjdk.org/browse/JDK-8246113) removed `PluggableContextTest`, yet forgot `MyContext`, and rendered it redundant. Remove `MyContext` too.

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Commit messages:
 - Remove unused `test/jdk/javax/script/MyContext.java`

Changes: https://git.openjdk.org/jdk/pull/25748/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25748&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359225
  Stats: 222 lines in 1 file changed: 0 ins; 222 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25748.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25748/head:pull/25748

PR: https://git.openjdk.org/jdk/pull/25748