db/update/Service: add SimpleDatabase reference

Don't use the global variables from the DatabaseSimple library.

src/db/update/Service.hxx

@@ -26,6 +26,8 @@
 #include "event/DeferredMonitor.hxx"
 #include "thread/Thread.hxx"
 
+class SimpleDatabase;
+
 /**
  * This class manages the update queue and runs the update thread.
  */
@@ -36,6 +38,8 @@ class UpdateService final : DeferredMonitor {
 		UPDATE_PROGRESS_DONE = 2
 	};
 
+	SimpleDatabase &db;
+
 	Progress progress;
 
 	bool modified;
@@ -53,7 +57,7 @@ class UpdateService final : DeferredMonitor {
 	UpdateWalk walk;
 
 public:
-	UpdateService(EventLoop &_loop);
+	UpdateService(EventLoop &_loop, SimpleDatabase &_db);
 
 	/**
 	 * Returns a non-zero job id when we are currently updating