cache the right variable

binary+depends is outdated; it's just command now

Change-Id: Ic4617d760585e53a485920e843627d3f9707d6a9
Reviewed-by: Qt Doc Bot <qt_docbot@qt-project.org>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>

mkspecs/features/qt_tool.prf

@@ -81,7 +81,6 @@ INSTALLS += target
         unset(added)
     }
     include($$TOOL_PRI)
-    for(var, $$list(binary depends)): \
-        cache(QT_TOOL.$${MODULE}.$$var, transient)
+    cache(QT_TOOL.$${MODULE}.command, transient)
 
 }