LibWeb: Combine background-repeat-x/y pseudo-properties

While right now this doesn't save much complexity, it will do once we
care about multiple background layers per node. Then, having a single
repeat value per layer will simplify things.

It also means we can remove the pseudo-property concept entirely! :^)

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -78,6 +78,7 @@
     ]
   },
   "background-repeat": {
+    "inherited": false,
     "initial": "repeat",
     "max-values": 2,
     "valid-identifiers": [
@@ -87,22 +88,8 @@
       "repeat-y",
       "round",
       "space"
-    ],
-    "longhands": [
-      "background-repeat-x",
-      "background-repeat-y"
     ]
   },
-  "background-repeat-x": {
-    "inherited": false,
-    "initial": "repeat",
-    "pseudo": true
-  },
-  "background-repeat-y": {
-    "inherited": false,
-    "initial": "repeat",
-    "pseudo": true
-  },
   "border": {
     "longhands": [
       "border-width",