do not start genesis data fetching periodically

From this point genesis data fetching will start and will
be retried on a task failure. Also, this PR disables genesis
data fetcher process by default because most our users won't
know that they should set chain spec for it.

apps/explorer/config/config.exs

@@ -27,7 +27,7 @@ config :explorer, Explorer.Counters.AverageBlockTime,
   enabled: true,
   period: average_block_period
 
-config :explorer, Explorer.ChainSpec.GenesisData, enabled: true, chain_spec_path: System.get_env("CHAIN_SPEC_PATH")
+config :explorer, Explorer.ChainSpec.GenesisData, enabled: false, chain_spec_path: System.get_env("CHAIN_SPEC_PATH")
 
 config :explorer, Explorer.Chain.Cache.BlockNumber, enabled: true
 

apps/explorer/lib/explorer/chain_spec/genesis_data.ex

@@ -18,7 +18,6 @@ defmodule Explorer.ChainSpec.GenesisData do
 
   @impl GenServer
   def init(_) do
-    :timer.send_interval(@interval, :import)
     Process.send_after(self(), :import, @interval)
 
     {:ok, %{}}