Delete ppapi/native_client, ppapi/nacl_irt and references to it.

BUG=40511454

Change-Id: Ib68b518c0706a35d8d2dda585a505c8fb3aa8791
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6669673
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Derek Schuff <dschuff@chromium.org>
Reviewed-by: Zijie He <zijiehe@google.com>
Cr-Commit-Position: refs/heads/main@{#1478292}
NOKEYCHECK=True
GitOrigin-RevId: 1b0188911ce436dd3dd50476c42b60fbc43c66c4