chore: Set Geth as default JSON RPC Variant (#10509)

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/variant.ex

@@ -113,16 +113,9 @@ defmodule EthereumJSONRPC.Variant do
   # credo:disable-for-next-line
   defp get_default_variant do
     case Application.get_env(:explorer, :chain_type) do
-      :optimism -> "geth"
-      :polygon_zkevm -> "geth"
-      :zetachain -> "geth"
-      :shibarium -> "geth"
-      :stability -> "geth"
-      :zksync -> "geth"
-      :arbitrum -> "geth"
       :rsk -> "rsk"
       :filecoin -> "filecoin"
-      _ -> "nethermind"
+      _ -> "geth"
     end
   end
 end