[ui] ImageGallery: do not reduce thumbnail resolution

As we rely on the thumbnails cache, the images are already downscaled at
a small resolution. So there is no more need to force a max resolution
on the Qml Image.

meshroom/ui/qml/ImageGallery/ImageDelegate.qml

@@ -109,7 +109,6 @@ Item {
                     asynchronous: true
                     autoTransform: true
                     fillMode: Image.PreserveAspectFit
-                    sourceSize: Qt.size(100, 100)
                 }
                 BusyIndicator {
                     anchors.centerIn: parent