[hotfix] Remove unnecessary method override for method invoke

[beliefer]

What is the purpose of the change

This PR aims to remove unnecessary method override for method invoke.
The interface TaskInvokable provides a method invoke show below.
void invoke() throws Exception;
As an implementation, AbstractInvokable overrides it. We could remove it.

Brief change log

Remove unnecessary method override for method invoke.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)

[davidradl]

trivial change

[flinkbot]

CI report:

• b57a348 Azure: SUCCESS

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[beliefer]

ping @StephanEwen cc @1996fanrui @GOODBOY008

[lsyldliu]

LGTM

[beliefer]

@lsyldliu @davidradl Thank you !