Use 'private-code' subcommand for wayland-scanner

Lots of warning messages started appearing, and it turns out
that the existing 'code' subcommand was deprecated. Simply using
private-code would be good enough.

Bug: 1030484
Test: build
Change-Id: I0c73c003de7a31d1b324170da37cdc3dacd022a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1955908Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722656}

third_party/wayland/wayland_scanner_wrapper.py

@@ -37,7 +37,8 @@ def main(argv):
     protocol_path = os.path.join(src_root, protocol)
     protocol_without_extension = protocol.rsplit(".", 1)[0]
     out_base_name = os.path.join(root_gen_dir, protocol_without_extension)
-    generate_code(cmd, "code", protocol_path, out_base_name + "-protocol.c")
+    generate_code(cmd, "private-code", protocol_path,
+                  out_base_name + "-protocol.c")
     generate_code(cmd, "client-header", protocol_path,
                   out_base_name + "-client-protocol.h")
     generate_code(cmd, "server-header", protocol_path,