stream: delete redundant code

In `Writable.prototype.end()`, `state.ending` is true after calling
`endWritable()` and it doesn't reset to false.

In `Writable.prototype.uncork()`, `state.finished` must be false
if `state.bufferedRequest` is true.

PR-URL: https://github.com/nodejs/node/pull/18145


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>