Move List styles to theme.json

[bgardner]

Per https://github.com/WordPress/gutenberg/pull/53602, it should be safe to move this to theme.json:

/* -- List -- */

.is-style-no-disc {
    list-style-type: none;
    padding-left: 0;
}

Per Gutenberg 16.8 RC1 (https://github.com/WordPress/gutenberg/pull/54981) confirmed this is working in theme.json. Will merge once it’s included in WP6.4 Beta or RC.

"core/list": {
    "css": "&.is-style-no-disc {list-style-type: none; padding-left: 0;}",
    "spacing": {
        "padding": {
            "left": "var(--wp--custom--spacing--gap)"
        }
    }
},