net: inline maybeDestroy()

`maybeDestroy()` is only called from the listener of the `'end'` event.
That event is only emitted after the socket is connected (after `UV_EOF`
is read) and after `socket.readable` is set to `false`.

PR-URL: https://github.com/nodejs/node/pull/27136


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>