[range.cartesian.view] Don't name unused template parameter (#6177)

Author: hewillk

source/ranges.tex

@@ -14982,7 +14982,7 @@
       (@\libconcept{bidirectional_range}@<@\exposid{maybe-const}@<Const, Vs>>
         && @\exposconcept{cartesian-product-common-arg}@<@\exposid{maybe-const}@<Const, Vs>>));
 
-  template<class First, class... Vs>
+  template<class First, class...>
   concept @\defexposconcept{cartesian-product-is-common}@ =                 // \expos
     @\exposconcept{cartesian-product-common-arg}@<First>;