You can remove any material overrides you created on a render layer and revert back to the material shader used in the master layer.
To remove a material override from an object in a render layer: method 1
 the
            object and select Remove Material Override. A
            list of material overrides for the selected layer appears in the menu.
  the
            object and select Remove Material Override. A
            list of material overrides for the selected layer appears in the menu. 
         
To remove a material override from an object in a render layer: method 2
 the
            material swatch and select Remove Material Override From.
            The menu lists all objects in the layer that use the material override.
  the
            material swatch and select Remove Material Override From.
            The menu lists all objects in the layer that use the material override. 
         
If a material is currently
               not used as a material override, the menu displays "There are no
               objects with override" when you   a material swatch
               and select Remove Material Override From.
  a material swatch
               and select Remove Material Override From.
            
