[FLINK-11316] [tests] Drop JarFileCreator

[tisonkun]

What is the purpose of the change

(Copy from JIRA)
Description
JarFileCreatorTest fails when run with Java 9. Because JarFileCreator is not used in production, the class and its tests can be deleted.

Acceptance Criteria

• JarFileCreator and JarFileCreatorTest are deleted
• Usage of JarFileCreator in ClassLoaderUtilsTest#testWithURLClassLoader is replaced with an alternative

Brief change log

• Delete JarFileCreator and JarFileCreatorTest
• Replace usage of JarFileCreator in ClassLoaderUtilsTest#testWithURLClassLoader with a specific util method.

Verifying this change

Basically it is a trivial code cleanup and we ensure ClassLoaderUtilsTest#testWithURLClassLoader still valid.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

cc @GJL

[GJL]

Thanks @tisonkun , I will have a look.

[tisonkun]

Thanks @GJL for being an assignee.

[aljoscha]

To me this looks good! @GJL can you confirm whether this will work with Java 9 (and future versions)?

[GJL]

@aljoscha ClassLoaderUtilsTest#testWithURLClassLoader passes with Java 9 now. If you think this PR is fine, please merge.

[GJL]

Merging myself...