Update source/lib-intro.tex

Co-authored-by: A. Jiang <[email protected]>

Author: tkoeppe

source/lib-intro.tex

@@ -1317,7 +1317,6 @@
 for any of these C headers:
 \libnoheader{complex.h},
 \libnoheader{iso646.h},
-\libnoheader{codecvt.h},
 \libnoheader{stdatomic.h},
 \libnoheader{stdbool.h},
 \libnoheader{stdnoreturn.h},