Update walkthrough.rst (ray-project#51019)

Remove a duplicated sentence

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---------

Signed-off-by: maofagui <maofg92@163.com>
Signed-off-by: Philipp Moritz <pcmoritz@gmail.com>
Co-authored-by: Philipp Moritz <pcmoritz@gmail.com>

doc/source/ray-core/walkthrough.rst

@@ -20,8 +20,6 @@ Ray Core provides a small number of core primitives (i.e., tasks, actors, object
     Ray has introduced an experimental API for high-performance workloads that is
     especially well suited for applications using multiple GPUs.
     See :ref:`Ray Compiled Graph <ray-compiled-graph>` for more details.
-
-    See :ref:`Ray Compiled Graph <ray-compiled-graph>` for more details.
 
 Getting Started
 ---------------