Styles: Apply correct style to default links

By default, links are underlined, and the underline is removed on hover. That's what the CSS that was previously removed did. By moving the CSS into theme.json, subsequent block settings can override this (and they do, see site title, etc).

Follow up to 3b02a3b

source/wp-content/themes/wporg-parent-2021/theme.json

@@ -936,14 +936,14 @@
 			},
 			"link": {
 				"typography": {
-					"textDecoration": "none"
+					"textDecoration": "underline"
 				},
 				"color": {
 					"text": "var(--wp--custom--link--color--text)"
 				},
 				":hover": {
 					"typography": {
-						"textDecoration": "underline"
+						"textDecoration": "none"
 					}
 				}
 			},