docs: kernel_include.py: Fix build with docutils 0.21.1

Recent docutils removed `reprunicode`, which was used to remove the
leading `u` from the repr output of Python 2's `unicode` type. For
Python 3, `reprunicode` was just an alias for `str`.

Signed-off-by: Jan Alexander Steffens (heftig) <[email protected]>

Author: heftig

Documentation/sphinx/kernel_include.py

@@ -97,7 +97,7 @@ def _run(self):
         # HINT: this is the only line I had to change / commented out:
         #path = utils.relative_path(None, path)
 
-        path = nodes.reprunicode(path)
+        path = str(path)
         encoding = self.options.get(
             'encoding', self.state.document.settings.input_encoding)
         e_handler=self.state.document.settings.input_encoding_error_handler