gh-104146: Purge dead code from Argument Clinic (#104680)

The following local variables were assigned but never used:

- line 551:  result
- line 1341: groups
- line 1431: default_return_converter
- line 1529: ignore_self
- line 1809: input_checksum
- line 4224: new'

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Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>