BUG: groupby.describe on a frame with MultiIndex describes groupings

[rhshadrach]

df1 = pd.DataFrame([[1, 2]], columns=["a", "b"])
gb1 = df1.groupby("a")
result1 = gb1.describe()
print(result1.to_string())
#       b                                  
#   count mean std  min  25%  50%  75%  max
# a                                        
# 1   1.0  2.0 NaN  2.0  2.0  2.0  2.0  2.0

columns = pd.MultiIndex.from_tuples(
    [("a", ""), ("b", "c")], names=["b", "c"]
)
df2 = pd.DataFrame([[1, 2]], columns=columns)
gb2 = df2.groupby("a")
result2 = gb2.describe()
print(result2.to_string())
# b     a                                       b                                  
# c                                             c                                  
#   count mean std  min  25%  50%  75%  max count mean std  min  25%  50%  75%  max
# a                                                                                
# 1   1.0  1.0 NaN  1.0  1.0  1.0  1.0  1.0   1.0  2.0 NaN  2.0  2.0  2.0  2.0  2.0

In the first case, the grouping a is not included in the results; in the second case the grouping a is. The grouping should not be described here.

[rhshadrach]

Closed by #50806