Call opcache_reset PHP function directly

[Girgias]

Combined with #1398 this should allow the removal of frankenphp_execute_php_function

[AlliBalliBaba]

Cgo has a weird bug where it will sometimes throw a warning if you have a function without return value and parameters.

This will throw a warning:
void frankenphp_reset_opcache(void)

This will not:
int frankenphp_reset_opcache(void)

[dunglas]

Thanks @Girgias