Replace deprecated xarray method .drop with .drop_sel in simple_storage

[brews]

dscim/src/dscim/menu/simple_storage.py

Line 134 in 8a870c3

anomaly = anomaly.drop(

xarray docs say that .drop is deprecated in favor of .drop_sel or other .drop_*s.

[brews]

Thought: We might need to update the minimum version allowed for xarray with this update.