Remove warning

[NikKovIos]

In code there is a warning: #warning("THIS CODE FOR FAST FIX, BECAUSE https://github.com/vapor/multipart-kit/issues/63 not accepted yet"). This MR already merged. How about to remove it?

[nerzh]

Yes, I know, but if this code works now, do you really want to change it? If so, you can fix it and make a pull request for it, but be sure to check all file methods after that