[C23] Update status page regarding FLT_MAX_EXP

N2843 was subsumed by N2882; we could probably consider removing
subsumed entries, but I've been leaving them to help folks looking at
the editor's report from various working drafts and wondering about the
changes.

Author: AaronBallman

clang/www/c_status.html

@@ -981,7 +981,7 @@ <h2 id="c2x">C23 implementation status</h2>
     <tr>
       <td>Clarification for max exponent macros</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2843.pdf">N2843</a></td>
-      <td class="unknown" align="center">Unknown</td>
+      <td class="na" align="center">Subsumed by N2882</td>
     </tr>
     <tr>
       <td>Clarification about expression transformations</td>