Device#Show page starts health checks instead of relying on extension

[jjcarstens]

The device show page still schedules health checks to be run despite that now being an extension.

Also, if the device has the extension enabled but the product has disabled the health extension, it still attempts to get health checks for a device which results in errors like these on device:

17:31:55.040 [error] GenServer NervesHubLink.Extensions terminating
** (ArgumentError) errors were found at the given arguments:

  * 1st argument: invalid destination

    (erts 15.2) :erlang.send(NervesHubLink.Extensions.Health, {:__extension_event__, "check", %{}})
    (nerves_hub_link 2.6.0) lib/nerves_hub_link/extensions/extensions.ex:206: NervesHubLink.Extensions.handle_cast/2
    (stdlib 6.2) gen_server.erl:2371: :gen_server.try_handle_cast/3
    (stdlib 6.2) gen_server.erl:2433: :gen_server.handle_msg/6
    (stdlib 6.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
Last message: {:"$gen_cast", {:handle_event, "health:check", %{}}}
State: %{extensions: %{"geo" => %{module: NervesHubLink.Extensions.Geo, version: "0.0.1", attached?: false, attach_ref: nil}, "health" => %{module: NervesHubLink.Extensions.Health, version: "0.0.1", attached?: false, attach_ref: nil}}}

I believe we need to remove the health check scheduling from the UI or at the very least ensure it is checking both the product and device level setting