Node Previews:

Removed USE_HIDDEN_PREVIEW from source code as it is now deprecated.
The feature was introduced during project mango to quickly hide previews, now that the previews are hidden by default this feature has no need.
Inside the DNA the flag is still visible in comment, this way no one will reuse that value as it could have some side effects

Jeroen & Monique
 - At Mind -

release/scripts/startup/bl_ui/space_node.py

@@ -395,7 +395,6 @@ class NODE_PT_quality(bpy.types.Panel):
         col.prop(tree, "use_two_pass")
         col.prop(tree, "use_viewer_border")
         col.prop(snode, "show_highlight")
-        col.prop(snode, "use_hidden_preview")
 
 
 class NODE_UL_interface_sockets(bpy.types.UIList):