Revert "Address the poor performance of the existing unique-name generation (#17944)"

This reverts commit 83202d8ad6.

# Conflicts:
#	src/Base/Tools.cpp
#	src/Base/Tools.h

src/Gui/Document.cpp

@@ -1938,7 +1938,7 @@ void Document::importObjects(const std::vector<App::DocumentObject*>& obj, Base:
     localreader->readEndElement("Document");
 
     // In the file GuiDocument.xml new data files might be added
-    if (localreader->hasFilenames())
+    if (!localreader->getFilenames().empty())
         reader.initLocalReader(localreader);
 }