admin-guide: remove mention of old button (#57)

Author: sjkoke

doc/admin-guide.rst

@@ -61,7 +61,7 @@ This tab allows you to export Experiments, items, or scheduled bookings in vario
 
 TAG MANAGER tab
 ===============
-This interface allows an Admin to edit existing Tags. For instance, if you have Tags called "RPE1" and "RPE-1" and you want all of the Tags to be in the form "RPE-1", find the "RPE1" Tag, click on it to edit it to "RPE-1", and click the Deduplicate button.
+This interface allows an Admin to edit existing Tags. For instance, if you have Tags called "RPE1" and "RPE-1" and you want all of the Tags to be in the form "RPE-1", find the "RPE1" Tag, click on it to edit it to "RPE-1".
 
 BATCH ACTIONS tab
 =================