REF: remove unnecessary PeriodIndex._get_indexer
hmm lots of things are failing here. maybe an ensure_indexer issue? worse: https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=53846&view=logs&j=acc1347f-8235-55b0-95c7-0e2189e61659&t=486f34f1-eda6-516a-fc5d-d8195128dacd

```
>   value = parse_timedelta_string(value)
E   TypeError: Expected unicode, got numpy.str_
``` > hmm lots of things are failing here. maybe an ensure_indexer issue?

i think i switched the order of a np.asarray/to_timedelta call, just tried re-ordering them