Update markdown-conversion-support.mdx (#24602)

Remove duplicate listing of `application/vnd.ms-excel`.

Author: abegehr

src/content/partials/workers-ai/markdown-conversion-support.mdx

@@ -68,7 +68,7 @@
 				`application/vnd.openxmlformats-officedocument.spreadsheetml.sheet`,
 				`application/vnd.ms-excel.sheet.macroenabled.12`,
 				`application/vnd.ms-excel.sheet.binary.macroenabled.12`,
-				`application/vnd.ms-excel`, `application/vnd.ms-excel`
+				`application/vnd.ms-excel`
 			</td>
 		</tr>
 		<tr>