Revert "Use Krita's engine to load previews for PSD files"

This reverts commit 48ca610a.

This made Krita try to access resources in a background thread,
which is not possible.

BUG:459512

libs/ui/utils/KisFileIconCreator.cpp

@@ -110,10 +110,7 @@ bool KisFileIconCreator::createFileIcon(QString path, QIcon &icon, qreal deviceP
             } else {
                 return false;
             }
-        } else if (mimeType == "image/tiff" ||
-                   mimeType == "image/x-tiff" ||
-                   mimeType == "image/vnd.adobe.photoshop") {
-
+        } else if (mimeType == "image/tiff" || mimeType == "image/x-tiff") {
             // Workaround for a bug in Qt tiff QImageIO plugin
             QScopedPointer<KisDocument> doc(KisPart::instance()->createTemporaryDocument());
             doc->setFileBatchMode(true);