CLEANUP: Destroy http_err_chunks members during deinit

To make the deinit function a proper inverse of the init function we need to
free the `http_err_chunks`:

    ==252081== 311,296 bytes in 19 blocks are still reachable in loss record 50 of 50
    ==252081==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==252081==    by 0x2727EE: http_str_to_htx (http_htx.c:914)
    ==252081==    by 0x272E60: http_htx_init (http_htx.c:1059)
    ==252081==    by 0x26AC87: check_config_validity (cfgparse.c:4170)
    ==252081==    by 0x155DFE: init (haproxy.c:2120)
    ==252081==    by 0x155DFE: main (haproxy.c:3037)

src/http_htx.c

@@ -1112,6 +1112,9 @@ static void http_htx_deinit(void)
 		LIST_DELETE(&http_rep->list);
 		release_http_reply(http_rep);
 	}
+
+	for (rc = 0; rc < HTTP_ERR_SIZE; rc++)
+		chunk_destroy(&http_err_chunks[rc]);
 }
 
 REGISTER_CONFIG_POSTPARSER("http_htx", http_htx_init);