[class.spaceship] Remove incorrect note.

Author: zygoloid

source/classes.tex

@@ -6861,12 +6861,6 @@
 then the return type is deduced as
 the common comparison type (see below) of
 $\tcode{R}_0$, $\tcode{R}_1$, $\dotsc$, $\tcode{R}_{n-1}$.
-\begin{note}
-Otherwise,
-the program will be ill-formed
-if the expression $\tcode{x}_i$ \tcode{<=>} $\tcode{x}_i$
-is not implicitly convertible to the declared return type for any $i$.
-\end{note}
 If the return type is deduced as \tcode{void},
 the operator function is defined as deleted.
 If the declared return type of