Exchanges: Remove bespoke pair upgrade handling and abstract Start/Run (#1424)

* Exchanges: Remove Pair upgrade handling

Now redundant behind #1401. These paths should never be met.

Several legacy coin upgrade paths being deprecated as well: ZUSD and CNY
Expecting any users with bad config from 3+ years ago would have to
reset anyway.

Also: At the time the intention of this was to upgrade the config
format.
However now, instead, it'd mostly serve to reset enabled pairs if
there's a config mistake, which doesn't feel right.

* Kraken: Fix typo in Kraken type struct

* Exchanges: Abstract exchange Start() and Run()

* Exchanges: Add test for abstracted Start

* Exchanges: Move Start to Bootstrap

* Simplify waitgroup usage
* Add call to exchange.Bootstrap to allow overide or supplementation

* Exchanges: Concurrent common bootstap actions

* Gateio: Remove incorrect Run in test

* GateIO: Fix pair dependencies in tests

This ensures that the pairs are initialised no more than needed and
kind-of just-in-time.
Better pattern might be to use a function to get these pairs when we
need them.

* Exchanges: Complete UpdatePairs before ExecLims

If we're going to update pairs, it needs to complete before we check for
limits to avoid errors on old pairs

* Exchanges: Remove Start and Run from tmpl

Since they're replaced by bootstrap now and shouldn't need customisation
normally

* Alphapoint: Move Start to Bootstrap

* GateIO: Fix linter shadow var

cmd/exchange_wrapper_coverage/main.go

@@ -32,18 +32,19 @@ func main() {
 
 	log.Printf("Loading exchanges..")
 	var wg sync.WaitGroup
-	for x := range exchange.Exchanges {
-		if exchange.Exchanges[x] == "ftx" {
+	for i := range exchange.Exchanges {
+		name := exchange.Exchanges[i]
+		if name == "ftx" {
 			log.Println("Skipping exchange FTX...")
 			continue
 		}
-		err = engine.Bot.LoadExchange(exchange.Exchanges[x], &wg)
-		if err != nil {
-			log.Printf("Failed to load exchange %s. Err: %s",
-				exchange.Exchanges[x],
-				err)
-			continue
-		}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if err := engine.Bot.LoadExchange(name); err != nil {
+				log.Printf("Failed to load exchange %s. Err: %s", name, err)
+			}
+		}()
 	}
 	wg.Wait()
 	log.Println("Done.")