Delete drop_broken_stuff auxiliary function

This function now actually throws an error, and does not seem to be necessary anymore?

@znicholls probably wrote this bit, so might want to double-check.

src/climate_assessment/harmonization/__init__.py

@@ -314,17 +314,6 @@ def run_harmonization(df, instance, prefix):
             for _, msdf in scenarios.groupby(["model", "scenario"])
         )
 
-    LOGGER.info("Hacking around some regression in aneris - pyam stack")
-
-    def drop_broken_stuff(indf):
-        out = indf.copy()
-        idx_length = len(out.index.names)
-        drop_levels = list(range(idx_length // 2, idx_length))
-        out.index = out.index.droplevel(drop_levels)
-
-        return out
-
-    scenarios_harmonized = [drop_broken_stuff(s) for s in scenarios_harmonized]
 
     LOGGER.info("Combining results")
     scenarios_harmonized = pd.concat(scenarios_harmonized).reset_index()