Styles: Remove or update workaround for CSS4 selectors

[ryelle]

In #111, CSS was added to fix the layout for browsers that don't support :where selectors.

wporg-main-2022/source/wp-content/themes/wporg-main-2022/src/style/style.scss

Lines 639 to 663 in baeab7f

	/*
	* Workaround for Gutenberg CSS4 selectors on older browsers.
	*
	* @link https://github.com/WordPress/gutenberg/issues/43723.
	*
	* Reproducing gutenberg_get_layout_style() isn't practical, so this just hardcodes the needed values.
	*
	* Remove this when the above issue is fixed in a stable release.
	*/
	body .is-layout-constrained > * {
	max-width: var(--wp--style--global--content-size);
	margin-left: auto !important;
	margin-right: auto !important;
	}
	body .is-layout-constrained > .alignwide {
	max-width: var(--wp--style--global--wide-size);
	}
	body .is-layout-constrained > .alignfull {
	max-width: unset;
	margin-left: unset !important;
	margin-right: unset !important;
	}

Since then, GB has continued to use :where frequently, though we haven't updated any other CSS, nor have we added this to any of the other child themes. :where has strong support now:

Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2021.
— MDN

Additionally the styles added by our workaround are impacting other layout options, like aligning content left.

With workaround, centered	Without workaround, left

I think it would be safe to remove this CSS, though if we need to still support non-:where browsers, we should find a way to update the code (and do we need to add this workaround to other places?)