perf_hooks: remove GC callbacks on zero observers count

When all existed PerformanceObserver instances removed for type `gc` GC
callbacks should be removed.

PR-URL: https://github.com/nodejs/node/pull/29444


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>