[MINOR] Remove unused method (#6713)

Signed-off-by: Simon Dudley <simon.dudley@consensys.net>

Author: siladu

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/mainnet/DefaultProtocolSchedule.java

@@ -54,16 +54,6 @@ protected DefaultProtocolSchedule(final DefaultProtocolSchedule protocolSchedule
     this.protocolSpecs = protocolSchedule.protocolSpecs;
   }
 
-  public ScheduledProtocolSpec specScheduledForBlock(final ProcessableBlockHeader blockHeader) {
-    return protocolSpecs.stream()
-        .filter(s -> s.isOnOrAfterMilestoneBoundary(blockHeader))
-        .findFirst()
-        .orElseThrow(
-            () ->
-                new IllegalStateException(
-                    "No protocol spec found for block " + blockHeader.getNumber()));
-  }
-
   @Override
   public ProtocolSpec getByBlockHeader(final ProcessableBlockHeader blockHeader) {
     checkArgument(