[Android] Remove aura tester entry in chromium.android.json.

The bot was removed a while ago.

BUG=
TBR=martiniss@chromium.org,stip@chromium.org

Review URL: https://codereview.chromium.org/1691563002

Cr-Commit-Position: refs/heads/master@{#374781}

testing/buildbot/chromium.android.json

 {
-  "Android Aura Tester (dbg)": {
-    "gtest_tests": [
-      {
-        "test": "base_unittests"
-      },
-      {
-        "test": "compositor_unittests"
-      },
-      {
-        "test": "content_unittests"
-      }
-    ]
-  },
   "Android GN Builder (dbg)": {
     "additional_compile_targets": [
       "blimp_tests",