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

gctscript/wrappers/gct/exchange/exchange_test.go

@@ -204,7 +204,7 @@ func setupEngine() (err error) {
 	em := engine.NewExchangeManager()
 	engine.Bot.ExchangeManager = em
 
-	return engine.Bot.LoadExchange(exchName, nil)
+	return engine.Bot.LoadExchange(exchName)
 }
 
 func cleanup() {