src: remove node namespace qualifiers

This commit removes unneccessary node namespace qualifiers in node.cc
for consistency.

PR-URL: https://github.com/nodejs/node/pull/18962


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>