Obsolete AggregateConstantKeyRule

Following CALCITE-1023, AggregateConstantKeyRule is a superset of AggregateProjectPullUpConstantsRule because it matches any RelNode whose output columns are constants, not just a Project.

This task is to check that AggregateConstantKeyRule does indeed have all required functionality, convert test cases to use it, mark AggregateProjectPullUpConstantsRule deprecated, and remove as much of its code as possible.

Or to obsolete AggregateConstantKeyRule if that is easier.