Unqueue invalid transactions when skipping (#13918)

The check was intially added by: https://github.com/paritytech/substrate/pull/5121

But a later pr fixed it properly: https://github.com/paritytech/substrate/pull/9789

TLDR: We don't need to check for skipped anymore, as we already remove all transactions that are
being unlocked by an invalid transactions and thus, we will not tag them as invalid directly because
the nonce for example is incorrect.

Fixes: https://github.com/paritytech/substrate/issues/13911