maintenance(www) remove unused dependencies (#25463)

Co-authored-by: Aisha Blake <[email protected]>

www/package.json

@@ -71,13 +71,11 @@
     "gatsby-transformer-yaml": "^2.4.10",
     "get-package-json-from-github": "^1.2.1",
     "graphql-request": "1.8.2",
-    "gray-percentage": "^2.0.0",
     "hex-rgb": "^4.1.0",
     "hex2rgba": "^0.0.1",
     "js-yaml": "^3.14.0",
     "lodash-es": "^4.17.15",
     "minimatch": "^3.0.4",
-    "mitt": "^1.2.0",
     "mousetrap": "^1.6.5",
     "parse-github-url": "^1.0.2",
     "prism-react-renderer": "^0.2.0",
@@ -94,9 +92,7 @@
     "react-instantsearch": "^5.7.0",
     "react-modal": "^3.11.2",
     "react-typography": "^1.0.0-alpha.4",
-    "rehype-react": "^3.1.0",
     "remove-markdown": "^0.3.0",
-    "slash": "^3.0.0",
     "slugify": "^1.4.4",
     "styled-system": "^5.1.5",
     "theme-ui": "^0.3.1",