src: harden running native `SetImmediate()`s slightly

Prevent mistakes like the one fixed by the previous commit
by destroying the callback immediately after it has been called.

PR-URL: https://github.com/nodejs/node/pull/31468
Refs: https://github.com/nodejs/node/pull/31386


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>