Do not process already compiled PVFs in the session before entering active set

[AndreiEres]

In #4791 we added logic for preparing PVFs if node is a validator in the next session. The implementation is ok for the entering the set for the first time, but then we can spend time on processing already prepared PVFs.

Quoting @sandreim #4791 (comment)

I think this just keeps decompressing needlessly if we are a validator intermittently: at session 1, then at session 2 we are no longer, but we are again at session 3.

All that was prepared for session 1 will be reset as soon as we go into session 2 (already_prepared_code_hashes is cleared). Is there a better way to check? Like query the PVF subsystem if it has it already ? Also I think the query needs to take into account the executor params which we are preparing with not just code hash.

[AndreiEres]

This issue will no longer be relevant after #5142 has been merged