USB: remove err() macro

I thought this had been removed years ago.  All in-kernel users of this
call have now been cleaned up and converted over to use dev_err()
instead, which is the correct thing to do.  Now that there are no users,
the macro can be removed so no one else accidentally starts to use it.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>