as_block depr warning on tab completion

[TomAugspurger]

In [13]: df = pd.Series([1, 2, 3])

In [14]: df.<TAB>
/Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/generic.py:3720: FutureWarning: as_blocks is deprecated and will be removed in a future version
  return self.as_blocks()

This came up before in #16409 and the fix is in #16414

[jreback]

hmm easy enough to remove deprecated functions from the dir entirely (this is what _dir_deletions does)