Trade ThumbnailProvider for NAM's mxc support

With libQuotient 0.9 NAM can handle mxc links (almost) natively, so we
don't need to use an image provider neither for avatars (dropped
earlier), nor for image thumbnails.

CMakeLists.txt

@@ -149,7 +149,6 @@ add_executable(${PROJECT_NAME} WIN32 MACOSX_BUNDLE)
 target_sources(${PROJECT_NAME} PRIVATE
     client/quaternionroom.cpp client/quaternionroom.h
     client/htmlfilter.cpp client/htmlfilter.h
-    client/thumbnailprovider.cpp client/thumbnailprovider.h
     client/activitydetector.cpp client/activitydetector.h
     client/dialog.cpp client/dialog.h
     client/logindialog.cpp client/logindialog.h

client/qml/TimelineItem.qml

@@ -418,7 +418,7 @@ Item {
                             : progressInfo.failed
                               ? ""
                               : content?.info.thumbnail_info && !autoload
-                                ? "image://thumbnail/" + content.thumbnailMediaId
+                                ? room.makeMediaUrl(eventId, content.info.thumbnail_url)
                                 : ""
                     maxHeight: chatView.height - textField.height -
                                authorLabel.height * !settings.timelineStyleIsXChat

client/timelinewidget.cpp

@@ -49,7 +49,6 @@ TimelineWidget::TimelineWidget(ChatRoomWidget* chatRoomWidget)
 
     setResizeMode(SizeRootObjectToView);
 
-    engine()->addImageProvider("thumbnail"_ls, makeThumbnailProvider(this));
     engine()->setNetworkAccessManagerFactory(&namFactory);
 
     auto* ctxt = rootContext();