chore: remove duplicate mdast-util-to-string in site package (#8287)

Author: icyJoseph

apps/site/package.json

@@ -98,7 +98,6 @@
     "handlebars": "4.7.8",
     "jsdom": "^27.0.0",
     "mdast-util-from-markdown": "^2.0.2",
-    "mdast-util-to-string": "^4.0.0",
     "nock": "^14.0.10",
     "remark-frontmatter": "^5.0.0",
     "stylelint": "16.24.0",