docs: disable data-sveltekit-preload-data with "off" instead of false

[alesvaupotic]

Late versions of Kit prefer off over false, as in:

Unexpected value for preload-data — should be one of "", "off", "tap", "hover"

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[teemingc]

There are currently plans to deprecate the "off" option in favour of "false" according to sveltejs/svelte#8638 and #10039

That being said, it seems odd that the preload link options do not accept "false" at the moment (despite the docs saying they do). Maybe they should? But what setting would take place if the value is "true"?

kit/packages/kit/src/runtime/client/utils.js

Lines 33 to 34 in 4e62135

	'preload-code': ['', 'off', 'tap', 'hover', 'viewport', 'eager'],
	'preload-data': ['', 'off', 'tap', 'hover'],

[benmccann]

I agree it'd be better to accept false than update the docs

[alesvaupotic]

False or off, as long as it behaves as documented without shouting at developer. :)