src: simplify uptime and ppid return values

This commit removes extraneous wrapping of return values
in Uptime() and GetParentProcessId().

PR-URL: https://github.com/nodejs/node/pull/24562


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jon Moss <me@jonathanmoss.me>