Trac #34565: Fix wrong link in the documentation of topological submanifolds

The link in the `OUTPUT` field of the docstring of
`TopologicalSubmanifold.open_subset` is corrected to
{{{:class:`TopologicalSubmanifold`}}}

URL: https://trac.sagemath.org/34565
Reported by: egourgoulhon
Ticket author(s): Eric Gourgoulhon
Reviewer(s): Kwankyu Lee

Author: Release Manager

src/sage/manifolds/topological_submanifold.py

@@ -294,8 +294,7 @@ def open_subset(self, name, latex_name=None, coord_def={}, supersets=None):
 
         OUTPUT:
 
-        - the open subset, as an instance of
-          :class:`~sage.manifolds.manifold.topological_submanifold.TopologicalSubmanifold`
+        - the open subset, as an instance of :class:`TopologicalSubmanifold`
 
         EXAMPLES::