Remove awkard workaround

src/km3io/offline.py

@@ -4,7 +4,6 @@ import warnings
 import uproot
 import numpy as np
 import awkward as ak
-import awkward._io  # workaround for https://github.com/scikit-hep/awkward-1.0/issues/968
 
 from .definitions import mc_header
 from .tools import cached_property, to_num, unfold_indices