Remove all blimp engine code

This CL deletes the //blimp/engine directory and related files.

List of things that are updated:
- Build files.
- Top-level presubmit file regarding ScopedAllowIO access.
- Resource IDs for grit resources for both blimp engine and client.
- Comments in files that refer to //blimp/engine.
- The client_engine_integration.py script and build config.
- Default GN arguments for the blimp engine (file is kept empty).

Documentation is not updated yet.

BUG=677556

Review-Url: https://codereview.chromium.org/2629743003
Cr-Original-Commit-Position: refs/heads/master@{#443730}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 790e4f0610545c7e41ab4642e7856b058687e1e6

args/blimp_engine.gn

@@ -1,29 +1 @@
-# GN args template for a blimp engine. Works within a docker container.
-#
-# Add import to arg.gn in out directory and run gn gen on the directory to use.
-# E.g. for out directory out/foo:
-# echo "import(\"//build/args/blimp_engine.gn\")" > out/foo/args.gn
-# gn gen out/foo
-#
-# This file contains Blimp engine build args common to both
-# official builds and personal development builds.
-# Use gn args to add your own build preference args.
-
-use_aura = true
-use_ozone = true
-ozone_auto_platforms = false
-ozone_platform = "headless"
-ozone_platform_headless = true
-metrics_use_blimp = true
-use_low_quality_image_interpolation = true
-use_external_popup_menu = true
-
-# Not available within docker container.
-use_alsa = false
-use_pulseaudio = false
-use_cups = false
-use_glib = false
-
-# udev is not supported on targeted platform and also not something that will
-# be used by Blimp Engine.
-use_udev = false
+# Placeholder until bots are updated.