[clang] [Docs] Document freestanding requirements (PR #132232)

[A. Jiang via cfe-commits]

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@@ -534,11 +534,6 @@ <h2 id="c2x">C23 implementation status</h2>
       <td class="full" align="center">Clang 16</td>
     </tr>
     <!-- Apr 2021 Papers -->
-    <tr>
-      <td>String functions for freestanding implementations</td>
-      <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2524.htm">N2524</a></td>
-      <td class="none" align="center">No</td>
-    </tr>
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frederick-vs-ja wrote:

I found that c_status.html is currently listing some library-only changes (e.g. [N2359](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2359.pdf) and possibly [N2951](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2951.htm)). Perhaps a thorough cleanup (in a later PR) is desired?

https://github.com/llvm/llvm-project/pull/132232