fix rebase

Author: jreback

doc/source/groupby.rst

@@ -126,16 +126,6 @@ We could naturally group by either the ``A`` or ``B`` columns or both:
    grouped = df.groupby('A')
    grouped = df.groupby(['A', 'B'])
 
-.. versionadded:: 0.20
-
-If we also have a MultiIndex on columns ``A`` and ``B``, we can group by all
-but the specified columns.
-
-.. ipython:: python
-
-   df2 = df.set_index(['A', 'B'])
-   grouped = df2.groupby(level=df2.index.names.difference(['B'])
-
 These will split the DataFrame on its index (rows). We could also split by the
 columns: