Agh, didn't mean to enable that

It's never worked

lib/msf/util/exe.rb

@@ -641,7 +641,7 @@ require 'msf/core/exe/segment_appender'
     opts[:exe_type] = :dll
 
     if opts[:inject]
-      self.to_win64pe(framework, code, opts)
+      raise RuntimeError, 'Template injection unsupported for x64 DLLs'
     else
       exe_sub_method(code,opts)
     end