Remove all blimp engine code

build/args/blimp_engine.gn

-# 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.