remove aura_builder target

It is an empty target that was there for compatibility with GYP.

Nothing uses it anymore and thus it can be removed now.

The changes to the build side were already done here ->
https://chromium.googlesource.com/chromium/tools/build/+/1ba4afe62e56408169d479018801c04a2d8335ec

BUG=601920

Change-Id: I442368cc860dce8778fd0d064ef99bb3a854be11
Reviewed-on: https://chromium-review.googlesource.com/516982Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thiago Farina <tfarina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#476307}

BUILD.gn

@@ -1014,15 +1014,6 @@ if (!is_ios && !is_android && !is_chromecast && !is_fuchsia) {
   }
 }
 
-# For compatibility with GYP. The linux_chromium_chromeos_rel_ng and
-# linux_chromium_chromeos_compile_rel_ng bots reference this target as
-# something to build, but all targets for those bots to compile are set
-# up differently.
-# TODO bug 601920: Remove reference to aura_builder on bot config and delete
-# this group.
-group("aura_builder") {
-}
-
 if (is_android) {
   group("optimize_gn_gen") {
     deps = [

testing/buildbot/gn_isolate_map.pyl

@@ -146,10 +146,6 @@
     "type": "raw",
     "args": [],
   },
-  "aura_builder": {
-    "label": "//:aura_builder",
-    "type": "additional_compile_target",
-  },
   "aura_unittests": {
     "label": "//ui/aura:aura_unittests",
     "type": "windowed_test_launcher",

testing/buildbot/manage.py

@@ -139,7 +139,6 @@ SKIP_GN_ISOLATE_MAP_TARGETS = {
 
   # These targets are listed only in build-side recipes.
   'All_syzygy',
-  'aura_builder',
   'blink_tests',
   'cast_shell',
   'cast_shell_apk',