repl: remove deprecated bufferedCommand property

This property is deprecated since Node.js v9.0.0 and to improve
maintainability of the REPL it is now removed.

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>

PR-URL: https://github.com/nodejs/node/pull/33286


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>