Remove obsolete read_entry_data method from class ComponentCatalogConnector

[ptitzler]

Closes #2514

What changes were proposed in this pull request?

• Remove deprecated method
• None of the built-in component catalog connectors are impacted because they don't utilize the deprecated method
• This change breaks https://github.com/ptitzler/examples/tree/main/component-catalog-connectors/airflow-example-components-connector. The connector will not be fixed because it is no longer supported.
• This change breaks https://github.com/ptitzler/examples/tree/main/component-catalog-connectors/kfp-example-components-connector. The connector will be marked as no longer supported in Elyra v4+.
• See related changes in Update Kubeflow Pipelines and Apache Airflow example connector documentation examples#118
• TODO: fix failing server tests
• • TODO: fix failing integration tests

How was this pull request tested?

1. Installed https://github.com/ptitzler/examples/tree/main/component-catalog-connectors/kfp-example-components-connector, which only implements the obsolete method. (elyra-examples-kfp-catalog==0.1.0)
2. Created an instance of that catalog connector in Elyra.
3. Confirmed that the expected error is logged.

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[kevin-bates]

I didn't take these changes for a spin, but they look good. Thanks @ptitzler.