added description instead of remove usage [ci skip]

actionpack/lib/action_controller/metal/renderers.rb

@@ -94,7 +94,7 @@ def self.add(key, &block)
 
     # This method is the opposite of add method.
     #
-    # Usage:
+    # To remove a csv renderer:
     #
     #   ActionController::Renderers.remove(:csv)
     def self.remove(key)

actionpack/lib/action_dispatch/http/mime_type.rb

@@ -211,7 +211,7 @@ def parse_data_with_trailing_star(input)
 
       # This method is opposite of register method.
       #
-      # Usage:
+      # To unregister a MIME type:
       #
       #   Mime::Type.unregister(:mobile)
       def unregister(symbol)