sim: standardize sim_create_inferior handling of argv a bit more

sim: standardize sim_create_inferior handling of argv a bit more

For targets that process argv in sim_create_inferior, improve the code:
- provide more details in the comment
- make the check for when to re-init more robust
- clean out legacy sim_copy_argv code

This will be cleaned up more in the future when we have a common inferior
creation function, but at least help new ports get it right until then.