Including DataConverter in FFI::Type::Builtin does not seem needed

* It's not included in FFI upstream.

Author: eregon

lib/truffle/truffle/ffi_backend/type.rb

@@ -55,8 +55,6 @@ def put_at(pointer, offset, value)
     end
 
     class Builtin < Type
-      include DataConverter # TODO: Unclear if needed
-
       attr_reader :name
 
       def initialize(name, nfi_type, size, alignment)