test: delete outdated fixtures/stdio-filter.js

PR-URL: nodejs#13712
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Alexey Orlenko <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Gibson Fahnestock <[email protected]>
Reviewed-By: Brian White <[email protected]>