Remove TOKEN_DROP

assets/parser.d.erb

@@ -23,7 +23,6 @@ class <%= @classname %>
 <% end %>
         _TOKEN_COUNT = <%= @grammar.tokens.size %>,
         _TOKEN_DECODE_ERROR = <%= TOKEN_DECODE_ERROR %>,
-        _TOKEN_DROP = <%= TOKEN_DROP %>,
     }
 
     struct Token

lib/propane.rb

@@ -28,9 +28,6 @@ class Propane
   # Decoding error.
   TOKEN_DECODE_ERROR = 0xFFFFFFFD
 
-  # Token ID for a "dropped" token.
-  TOKEN_DROP = 0xFFFFFFFE
-
   class Error < RuntimeError
   end