Remove duplicated navigation_with_keys in docs config

[Illviljan]

Fixes:

Running Sphinx v6.2.1

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/8387/lib/python3.10/site-packages/sphinx/config.py", line 353, in eval_config_file
    code = compile(f.read(), filename.encode(fs_encoding), 'exec')
  File "/home/docs/checkouts/readthedocs.org/user_builds/xray/checkouts/8387/doc/conf.py", line 240
    navigation_with_keys=False,
    ^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: keyword argument repeated: navigation_with_keys

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/8387/lib/python3.10/site-packages/sphinx/cmd/build.py", line 280, in build_main
    app = Sphinx(args.sourcedir, args.confdir, args.outputdir,
  File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/8387/lib/python3.10/site-packages/sphinx/application.py", line 207, in __init__
    self.config = Config.read(self.confdir, confoverrides or {}, self.tags)
  File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/8387/lib/python3.10/site-packages/sphinx/config.py", line 177, in read
    namespace = eval_config_file(filename, tags)
  File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/8387/lib/python3.10/site-packages/sphinx/config.py", line 357, in eval_config_file
    raise ConfigError(msg % err) from err
sphinx.errors.ConfigError: There is a syntax error in your configuration file: keyword argument repeated: navigation_with_keys (conf.py, line 240)


Configuration error:
There is a syntax error in your configuration file: keyword argument repeated: navigation_with_keys (conf.py, line 240)
Command time: 0s Return: 2

Seen in #8387