[jdk8u-dev] RFR: 8179457: Remove demo/jvmti tests

[SendaoYan]

Hi all,

This is backport of [JDK-8179457](https://bugs.openjdk.org/browse/JDK-8179457) from jdk11u-dev to jdk8u-dev. The demos themselves have been removed. The tests are only testing the demos and does not seem to provide any other useful product testing. This PR remove demo/jvmti tests. Test-fix only, no risk.

Below files can not backport  cleanly:

1. File jdk/test/demo/jvmti/Context.java touch by JDK-7027502 in jdk11u-dev before JDK-8179457
2. File jdk/test/demo/jvmti/DemoRun.java touch by JDK-8076471/JDK-8071464 in jdk11u-dev before JDK-8179457
3. File jdk/test/demo/jvmti/minst/MinstTest.java touch by JDK-8078896 in jdk11u-dev before JDK-8179457
4. File jdk/test/ProblemList.txt has different context between jdk11u-dev and jdk8u-dev.

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Commit messages:
 - remove 6988950 and 7027502
 - Backport 7ebbf0f8404eb17b70806f4fb7cc289470d31b2e

Changes: https://git.openjdk.org/jdk8u-dev/pull/624/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=624&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8179457
  Stats: 973 lines in 15 files changed: 0 ins; 972 del; 1 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/624.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/624/head:pull/624

PR: https://git.openjdk.org/jdk8u-dev/pull/624