[diff.mods.to.headers] Delete statement that C headers are deprecated.

This deletion should have been part of P2340R1.

Author: tkoeppe

source/compatibility.tex

@@ -2794,7 +2794,7 @@
 \pnum
 For compatibility with the C standard library\indextext{library!C standard},
 the \Cpp{} standard library provides the C headers enumerated
-in~\ref{support.c.headers}, but their use is deprecated in \Cpp{}.
+in~\ref{support.c.headers}.
 
 \pnum
 There are no \Cpp{} headers for the C standard library's headers