docs: sphinx-build-wrapper: stop setting kerneldoc_bin for Sphinx

Now that the Sphinx build does not use the kerneldoc_bin configuration
variable, we shouldn't try to set it in the build wrapper or we get a nifty
warning:

  WARNING: unknown config value 'kerneldoc_bin' in override, ignoring

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: Jonathan Corbet

tools/docs/sphinx-build-wrapper

@@ -750,7 +750,6 @@ class SphinxBuilder:
 
             build_args = args + [
                 "-d", doctree_dir,
-                "-D", f"kerneldoc_bin={kerneldoc}",
                 "-D", f"version={self.kernelversion}",
                 "-D", f"release={self.kernelrelease}",
                 "-D", f"kerneldoc_srctree={self.srctree}",