DEPR: frequencies.getOffset
`tseries.frequencies` aliases `getOffset = get_offset`.  That has been around and unused for a while, should be deprecated and eventually removed.

`tseries.offsets.generate_range` has a kwarg `time_rule` with docstring description:
```
    time_rule : (legacy) name of DateOffset object to be used, optional
        Corresponds with names expected by tseries.frequencies.get_offset
```

If this is legacy behavior, it should be deprecated and eventually removed.