staking miner: remove needless queue check (#6221)

* staking miner: remove needless queue check

If the queue is full and the "mined solution" is better than solutions in the queue according to the "strategy"
then the solution with worse score will be kicked out from the queue.

Thus, the check can be removed completly.

* fix compile warns

polkadot/utils/staking-miner/src/main.rs

@@ -253,7 +253,6 @@ enum Error<T: EPM::Config> {
 	AlreadySubmitted,
 	VersionMismatch,
 	StrategyNotSatisfied,
-	QueueFull,
 	Other(String),
 }