{MySQL} Hide backup export command (#32440)

Author: honghr

src/azure-cli/azure/cli/command_modules/mysql/commands.py

@@ -202,7 +202,9 @@ def load_command_table(self, _):
 
     with self.command_group('mysql flexible-server export', mysql_flexible_export_sdk,
                             custom_command_type=mysql_custom,
-                            client_factory=cf_mysql_flexible_export, is_preview=True) as g:
+                            client_factory=cf_mysql_flexible_export,
+                            is_preview=True,
+                            deprecate_info=self.deprecate(hide=True)) as g:
         g.custom_command('create', 'flexible_server_export_create')
 
     with self.command_group('mysql flexible-server identity', mysql_flexible_servers_sdk,