[cmp.common] Remove unnecessary "std::" before strong_ordering

Author: eisenwave

source/support.tex

@@ -5323,7 +5323,7 @@
 \keyword{void} if any element of \tcode{Ts}
 is not a comparison category type.
 \begin{note}
-This is \tcode{std::strong_ordering} if the expansion is empty.
+This is \tcode{strong_ordering} if the expansion is empty.
 \end{note}
 \end{itemdescr}