fix some XDeclaredButNotUsed hints (#1027)

beacon_chain/block_pool.nim

@@ -226,7 +226,6 @@ proc init*(T: type BlockPool, db: BeaconChainDB,
       tmpState.data.data.current_justified_checkpoint.epoch.compute_start_slot_at_epoch()
     justifiedHead = headRef.atSlot(justifiedSlot)
     head = Head(blck: headRef, justified: justifiedHead)
-    justifiedBlock = db.getBlock(justifiedHead.blck.root).get()
 
   doAssert justifiedHead.slot >= finalizedHead.slot,
     "justified head comes before finalized head - database corrupt?"

beacon_chain/eth2_network.nim

@@ -479,7 +479,7 @@ proc handleIncomingStream(network: Eth2Node,
   mixin callUserHandler, RecType
 
   type MsgRec = RecType(MsgType)
-  const msgName = typetraits.name(MsgType)
+  const msgName {.used.} = typetraits.name(MsgType)
 
   ## Uncomment this to enable tracing on all incoming requests
   ## You can include `msgNameLit` in the condition to select

beacon_chain/ssz.nim

@@ -34,7 +34,6 @@ when defined(serialization_tracing):
 const
   bytesPerChunk = 32
   bitsPerChunk = bytesPerChunk * 8
-  maxChunkTreeDepth = 25
   defaultMaxObjectSize = 1 * 1024 * 1024
 
 type