Theme export: Fix broken spacingScale export

[glendaviesnz]

What?

Removes a spacing presets config that was added in error.

Why?

Fixes: #44546

How?

Removes the spacing presets config for spacingScale as only spacingSizes should be defined.

Testing Instructions

• Under theme.json settings.spacing define a "spacingScale": { "steps": 0} array in a theme.json
• Export the theme from the site editor
• Make sure the exported theme.json includes the spacingScale
• Check that the spacing presets still work as expected in post editor, site editor and frontend

Screenshots or screencast

Before:

After:

[glendaviesnz]

Backport PR here

[glendaviesnz]

Trac ticket: https://core.trac.wordpress.org/ticket/56684

[tellthemachines]

Testing this change with TT3 I can confirm that the disappearance of spacingScale and the fluid setting in typography are fixed, but the slugs in spacingSizes are still being exported without quotes. I just enabled TT3 and exported from the site editor - is there any other testing step I'm missing?

[dream-encode]

Merged into core in https://core.trac.wordpress.org/changeset/54360.

[glendaviesnz]

Reopened as we need this fix in GB trunk as well

[ramonjd]

LGTM

"spacing": {
	"spacingScale": {
		"steps": 0
	},
	"spacingSizes": [
		{
			"name": "1",
			"size": "clamp(1.5rem, 5vw, 2rem)",
			"slug": 30
		},
		{
			"name": "2",
			"size": "clamp(1.8rem, 1.8rem + ((1vw - 0.48rem) * 2.885), 3rem)",
			"slug": 40
		},
		{
			"name": "3",
			"size": "clamp(2.5rem, 8vw, 6.5rem)",
			"slug": 50
		},
		{
			"name": "4",
			"size": "clamp(3.75rem, 10vw, 7rem)",
			"slug": 60
		},
		{
			"name": "5",
			"size": "clamp(5rem, 5.25rem + ((1vw - 0.48rem) * 9.096), 8rem)",
			"slug": 70
		},
		{
			"name": "6",
			"size": "clamp(7rem, 14vw, 11rem)",
			"slug": 80
		}
	],

Slug ints fixed in #44589

[michalczaplinski]

Cherry-picked for the 6.1 release in #44656