fix: drop unused deps

Author: Yukaii

package-lock.json

@@ -285,8 +285,6 @@
     "markdown-it-table-of-contents": "^0.4.4",
     "mathjax": "^3.0.1",
     "mathjax-full": "^3.0.1",
-    "mobx": "^5.15.4",
-    "node-fetch": "^2.6.7",
     "react": "^17.0.2",
     "react-vsc-treeview": "^0.2.3",
     "string": "git+ssh://[email protected]/hackmdio/string.js.git#a68176b3d",