BUG: Attributes of DataFrameGroupBy when subset to a series 
xref #9959 

When subsetting the columns of a dataframe after a groupby to a series:

    df = pd.DataFrame({'a': [1], 'b': [2], 'c': [3]}).set_index('a')
    g = df.groupby('a')['b']

the public-facing groupby arguments  `axis` and `as_index` are not passed on to the resulting `SeriesGroupBy`.

I think the following two examples should probably behave the same:

    g = df.groupby('a', as_index=False)['b']
    g2 = df['b'].groupby('a', as_index=False)

but the first produces
````
   b
0  2
````

And the 2nd deliberately raises `TypeError: as_index=False only valid with DataFrame`.

Note that the arguments `axis` and `as_index` are only meant for DataFrames, and as such, I think a line such as

    g = df.groupby('a', as_index=False)['b']

should raise.