lsst.verify.MetricTask as written based on an alpha release of the Gen 3 framework, and borrows its PipelineTask API to let subclasses seamlessly transition from Gen 2 to Gen 3. However, the final Gen 3 framework does not have two of the methods assumed by the original MetricTask design, namely adaptArgsAndRun and getInputDatasetTypes. While these methods are acceptable in gen2tasks.MetricTask, which will eventually be removed, subclasses that are supposed to be Gen 2/Gen 3 agnostic must not be required to implement these methods and must not depend on them for functionality.

This ticket covers the following work:

• Rewrite PpdbMetricTask to no longer have a custom adaptArgsAndRun, while leaving the API seen by subclasses unchanged.
• Replace all calls to adaptArgsAndRun in the metrics test suites of ip_diffim, ap_association, and verify, as well as in the common test code provided by verify, except where the code is only applicable to Gen 2.
• Remove references to overriding adaptArgsAndRun in the MetricTask and MetadataMetricTask documentation.
• Replace all calls to getInputDatasetTypes in test code.
• Remove references to getInputDatasetTypes from the documentation of PpdbMetricTask