Update sys.path references (#50466)

lib/spack/docs/conf.py

@@ -35,7 +35,6 @@
 if not os.path.exists(link_name):
     os.symlink(os.path.abspath("../../.."), link_name, target_is_directory=True)
 sys.path.insert(0, os.path.abspath("_spack_root/lib/spack/external"))
-sys.path.insert(0, os.path.abspath("_spack_root/lib/spack/external/_vendoring"))
 sys.path.append(os.path.abspath("_spack_root/lib/spack/"))
 
 # Add the Spack bin directory to the path so that we can use its output in docs.