Remove bounds from `PrevalidateAttests` struct definition (#2886)
Removing some bounds as it came up in https://github.com/paritytech/polkadot-sdk/pull/2726 while still keeping `Send + Sync` capabilities. --------- Signed-off-by: Oliver Tale-Yazdi <[email protected]> Co-authored-by: Bastian Köcher <[email protected]>