fixup! use a waitgroup to wait for reserve holders of MFiles before u…

…nmapping

src/lavinmq/mfile.cr

@@ -190,11 +190,6 @@ class MFile < IO
     raise RuntimeError.from_errno("msync") if code < 0
   end
 
-  # def finalize
-  #   LibC.close(@fd) if @fd > -1
-  #   LibC.munmap(@buffer, @capacity) unless @buffer.null?
-  # end
-
   def write(slice : Bytes) : Nil
     size = @size
     new_size = size + slice.size