Timestamp.replace should take freq kwarg
```
>>> ts.replace(freq=None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pandas/_libs/tslibs/timestamps.pyx", line 840, in pandas._libs.tslibs.timestamps.Timestamp.replace
    def replace(self, year=None, month=None, day=None,
TypeError: replace() got an unexpected keyword argument 'freq'
```