Revert "Add linkup command to improve link functionality" (#4439)

This reverts commit 2504f6fce4.

ci/build/npm-postinstall.sh

@@ -66,12 +66,6 @@ main() {
     echo "Failed to download cloud agent; --link will not work"
   fi
 
-  if curl -fsSL "https://storage.googleapis.com/coder-link-releases/latest/linkup-$OS-$ARCH" -o ./lib/linkup; then
-    chmod +x ./lib/linkup
-  else
-    echo "Failed to download Link agent; the Link extension will not work"
-  fi
-
   if ! vscode_yarn; then
     echo "You may not have the required dependencies to build the native modules."
     echo "Please see https://github.com/cdr/code-server/blob/master/docs/npm.md"