[fs.class.path.general] Defuse cross-reference to POSIX

Fixes ISO/CS comment (C++23 proof)

Author: jensmaurer

source/iostreams.tex

@@ -13592,11 +13592,8 @@
 \pnum
 \defnx{Pathname resolution}{pathname resolution}
 is the operating system dependent mechanism for resolving
-a pathname to a particular file in a file hierarchy. There may be multiple
-pathnames that resolve to the same file.
-\begin{example}
-POSIX specifies the mechanism in section 4.12, Pathname resolution.
-\end{example}
+a pathname to a particular file in a file hierarchy (see POSIX, section 4.12).
+There may be multiple pathnames that resolve to the same file.
 
 \begin{codeblock}
 namespace std::filesystem {