Set styleCheck to error for nimbus_verified_proxy + some cleanup (#2297)

nimbus_verified_proxy/nim.cfg

@@ -18,6 +18,6 @@
 -d:"libp2p_pki_schemes=secp256k1"
 
 --styleCheck:usages
---styleCheck:hint
+--styleCheck:error
 --hint[ConvFromXtoItselfNotNeeded]:off
 --hint[Processing]:off

nimbus_verified_proxy/nimbus_verified_proxy.nim

@@ -8,7 +8,7 @@
 {.push raises: [].}
 
 import
-  std/[atomics, json, os, strutils],
+  std/[json, os, strutils],
   chronicles,
   chronos,
   confutils,
@@ -204,7 +204,7 @@ proc run*(
         info "New LC finalized header", finalized_header = shortLog(forkyHeader)
         if headerCallback != nil:
           try:
-            headerCallback(Json.encode(forkyHeader), 0)
+            headerCallback(cstring(Json.encode(forkyHeader)), 0)
           except SerializationError as e:
             notice "finalizedHeaderCallback exception"
 
@@ -217,7 +217,7 @@ proc run*(
         optimisticProcessor.setOptimisticHeader(forkyHeader.beacon)
         if headerCallback != nil:
           try:
-            headerCallback(Json.encode(forkyHeader), 1)
+            headerCallback(cstring(Json.encode(forkyHeader)), 1)
           except SerializationError as e:
             notice "optimisticHeaderCallback exception"
 

nimbus_verified_proxy/rpc/rpc_utils.nim

@@ -9,7 +9,6 @@
 
 import
   std/typetraits,
-  chronicles, # Added for generic sandwich that hits in core_db :(
   eth/common/eth_types as etypes,
   eth/[trie, rlp],
   stint,