[meta.reflection.extract] Remove second "constexpr if"

Fixes NB US 113-173 (C++26 CD).

Author: JeffGarland

source/meta.tex

@@ -5987,7 +5987,7 @@
 \begin{codeblock}
 if constexpr (is_reference_type(^^T)) {
   return @\exposid{extract-ref}@<T>(r);
-} else if constexpr (is_nonstatic_data_member(r) || is_function(r)) {
+} else if (is_nonstatic_data_member(r) || is_function(r)) {
   return @\exposid{extract-member-or-function}@<U>(r);
 } else {
   return @\exposid{extract-value}@<U>(constant_of(r));