Remove dead code in oj_hash_init

[peterzhu2118]

No description provided.

[ohler55]

I believe classes can move hence the need for the registration.

[peterzhu2118]

rb_gc_register_address takes a pointer to a VALUE, but cache_class is allocated on the stack which means that it becomes invalid memory the moment the function returns. You can see the implementation here.

This function doesn't seem to be using cache_class in any way that is unsafe for compaction, so we don't need to pin it (i.e. tell compaction that this object cannot move).

[ohler55]

You are correct. Thanks.