move cosmetic module docs to private modules

Author: ItsNature

docs/developers/modules/_meta.json

@@ -6,7 +6,6 @@
     "coloredfire": "Colored Fire",
     "combat": "Combat",
     "cooldown": "Cooldown",
-    "cosmetic": "Cosmetic",
     "entity": "Entity",
     "glint": "Glint",
     "glow": "Glow",