Remove sink from stream

someProcess.stderr.pipeTo(
  new WritableStream({
    write(chunk, controller) {
      if (someCondition()) {
        // how the heck do i "undo" this sink?
        // i want to stop processing here, and i don't care what
        // happens to stderr after this point.
      }
    },
  }),
);

someProcess.stderr.pipeTo(
  new WritableStream({
    write(chunk, controller) {
      if (someCondition()) {
        // how the heck do i "undo" this sink?
        // i want to stop processing here, and i don't care what
        // happens to stderr after this point.
      }
    },
  }),
);