Muscat variation: fix rubik reference (#6757)

* Fix reference to rubik.

* Remove it instead.

muscat/styles/midnight.json

@@ -522,7 +522,6 @@
 			},
 			"heading": {
 				"typography": {
-					"fontFamily": "var(--wp--preset--font-family--rubik)",
 					"fontStyle": "normal",
 					"fontWeight": "400",
 					"letterSpacing": "-1px",