[6.x] Revert "fs: fix options.end of fs.ReadStream()"

This reverts commit df038ad9.

Some people were relying on the behavior of this.start being able to be undefined, whereas after the change it is being set to 0.

Fixes: https://github.com/nodejs/node/issues/19240: Refs: https://github.com/nodejs/node/pull/18121

/cc @wankdanker @MoonBall @nodejs/lts