core: remove stupid isbinaryfile

packages/hydrooj/package.json

@@ -29,7 +29,6 @@
         "fs-extra": "^11.1.0",
         "graphql": "^16.6.0",
         "graphql-scalars": "1.20.1",
-        "isbinaryfile": "^5.0.0",
         "js-yaml": "^4.1.0",
         "koa": "^2.14.1",
         "koa-body": "^6.0.1",