Remove the docs on using kitty config infrastructure in custom kittens

That config infrastructure isnt really maintained anymore since
builtin kittens have now been almost all ported to Go. So in future
people should just use any of python's stdlib config modules such as
tomllib to store and retrieve their kitten configs.

docs/kittens/custom.rst

@@ -298,108 +298,6 @@ So if you run kitty from another kitty instance, the output will be visible
 in the first kitty instance.
 
 
-Adding options to kittens
-----------------------------
-
-If you would like to use kitty's config framework to make your kittens
-configurable, you will need some boilerplate. Put the following files in the
-directory of your kitten.
-
-:file:`kitten_options_definition.py`
-
-.. code-block:: python
-
-    from kitty.conf.types import Action, Definition
-
-    definition = Definition(
-        '!kitten_options_utils',
-        Action(
-            'map', 'parse_map',
-            {'key_definitions': 'kitty.conf.utils.KittensKeyMap'},
-            ['kitty.types.ParsedShortcut', 'kitty.conf.utils.KeyAction']
-        ),
-    )
-
-    agr = definition.add_group
-    egr = definition.end_group
-    opt = definition.add_option
-    map = definition.add_map
-
-    # main options {{{
-    agr('main', 'Main')
-
-    opt('some_option', '33',
-        option_type='some_option_parser',
-        long_text='''
-    Help text for this option
-    '''
-        )
-    egr()  # }}}
-
-    # shortcuts {{{
-    agr('shortcuts', 'Keyboard shortcuts')
-
-    map('Quit', 'quit q quit')
-    egr()  # }}}
-
-
-:file:`kitten_options_utils.py`
-
-.. code-block:: python
-
-    from kitty.conf.utils import KittensKeyDefinition, key_func, parse_kittens_key
-
-    func_with_args, args_funcs = key_func()
-    FuncArgsType = Tuple[str, Sequence[Any]]
-
-    def some_option_parser(val: str) -> int:
-        return int(val) + 3000
-
-    def parse_map(val: str) -> Iterable[KittensKeyDefinition]:
-        x = parse_kittens_key(val, args_funcs)
-        if x is not None:
-            yield x
-
-Then run::
-
-    kitty +runpy 'from kitty.conf.generate import main; main()' /path/to/kitten_options_definition.py
-
-You can parse and read the options in your kitten using the following code:
-
-.. code-block:: python
-
-    from .kitten_options_types import Options, defaults
-    from kitty.conf.utils import load_config as _load_config, parse_config_base
-    from typing import Optional, Iterable, Dict, Any
-
-    def load_config(*paths: str, overrides: Optional[Iterable[str]] = None) -> Options:
-        from .kitten_options_parse import  (
-            create_result_dict, merge_result_dicts, parse_conf_item
-        )
-
-        def parse_config(lines: Iterable[str]) -> Dict[str, Any]:
-            ans: Dict[str, Any] = create_result_dict()
-            parse_config_base(
-                lines,
-                parse_conf_item,
-                ans,
-            )
-            return ans
-
-        overrides = tuple(overrides) if overrides is not None else ()
-        opts_dict, found_paths = _load_config(defaults, parse_config, merge_result_dicts, *paths, overrides=overrides)
-        opts = Options(opts_dict)
-        opts.config_paths = found_paths
-        opts.all_config_paths = paths
-        opts.config_overrides = overrides
-        return opts
-
-See `the code
-<https://github.com/kovidgoyal/kitty/tree/master/kittens/diff/main.py>`__
-for the builtin :doc:`diff kitten </kittens/diff>` for examples of creating more
-options and keyboard shortcuts.
-
-
 Developing builtin kittens for inclusion with kitty
 ----------------------------------------------------------