multi: Rename shutdownWg to wg.

The more verbose name was helpful in the past when some code was
handling more than one waitgroup, however that is no longer the case due
to refactoring so reverting to the more concise name makes sense.

cmd/vspd/main.go

@@ -109,30 +109,30 @@ func run() int {
 	}
 
 	// WaitGroup for services to signal when they have shutdown cleanly.
-	var shutdownWg sync.WaitGroup
+	var wg sync.WaitGroup
 
 	// Start the webapi server.
-	shutdownWg.Add(1)
+	wg.Add(1)
 	go func() {
 		api.Run(ctx)
-		shutdownWg.Done()
+		wg.Done()
 	}()
 
 	// Start vspd.
 	vspd := vspd.New(cfg.network, log, db, dcrd, wallets, blockNotifChan)
-	shutdownWg.Add(1)
+	wg.Add(1)
 	go func() {
 		vspd.Run(ctx)
-		shutdownWg.Done()
+		wg.Done()
 	}()
 
 	// Periodically write a database backup file.
-	shutdownWg.Add(1)
+	wg.Add(1)
 	go func() {
 		for {
 			select {
 			case <-ctx.Done():
-				shutdownWg.Done()
+				wg.Done()
 				return
 			case <-time.After(cfg.BackupInterval):
 				err := db.WriteHotBackupFile()
@@ -145,7 +145,7 @@ func run() int {
 
 	// Wait for shutdown tasks to complete before running deferred tasks and
 	// returning.
-	shutdownWg.Wait()
+	wg.Wait()
 
 	return 0
 }