Gatekeeping feed engine seems unnecessary now

[MrTimbones]

Each app has a configuration of feeds that it needs, and (optionally) a list of engines that it will accept for each feed:

config.app = {
    "title":{"type":"value", "default":"OCTOPUS AGILE", "name": "Title", "description":"Optional title for app"},
    "import":{"optional":true, "type":"feed", "autoname":"import", "engine":"5"},
    "import_kwh":{"type":"feed", "autoname":"import_kwh", "engine":5},
    "use_kwh":{"optional":true, "type":"feed", "autoname":"use_kwh", "engine":5},
    "solar_kwh":{"optional":true, "type":"feed", "autoname":"solar_kwh", "engine":5},
    "meter_kwh_hh":{"optional":true, "type":"feed", "autoname":"meter_kwh_hh", "engine":5},
};

The engine is set to "5" for the majority of feeds across the apps, and so prevents using anything other than PHPFINA. This is done by engine_check() within Lib/appconf.js.

Since recent work on the feed engines, they can pretty much all do everything that the apps require, so it no longer seems necessary to restrict the user from certain type of feeds. I propose that the engine check is removed.

[MrTimbones]

Engine requirement was removed from My Heatpump app by ea54b2f; most other apps don't have it and work fine with any type of feed.