Cleanup: Remove aura_builder target.

Now that Aura is the default for a long time on Linux, this does not
seem to be necessary anymore.

BUG=None
TEST=trybots
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/916713002

Cr-Original-Commit-Position: refs/heads/master@{#315765}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c1dcb9c1ba668d4948441d956709ab9747b5c65d

all.gyp

@@ -1329,21 +1329,6 @@
           ],
         },
       ],  # targets
-    }, {
-      'conditions': [
-        ['OS=="linux"', {
-          # TODO(thakis): Remove this once the linux gtk bot no longer references
-          # it (probably after the first aura release on linux), see r249162
-          'targets': [
-            {
-              'target_name': 'aura_builder',
-              'type': 'none',
-              'dependencies': [
-                '../chrome/chrome.gyp:chrome',
-              ],
-            },
-          ],  # targets
-      }]], # OS=="linux"
     }], # "use_aura==1"
     ['test_isolation_mode != "noop"', {
       'targets': [